github actions: Update to Android NDK 27c

Github actions continuous integration builds were failing
for Android targets because the specified `android.toolchain.cmake`
file was not available on the specified runner.

Github documents the runner images has having the lastest
stable NDK as well as the previous two LTS releases. We
were specifying 25.2.9519653, first released in 2022.
https://github.com/actions/runner-images/blob/releases/ubuntu24/20250629/README.md#software-and-image-support

Instead specify r27c, released in 2024 and still the
current LTS release.
https://developer.android.com/ndk/downloads/revision_history

Also move the version to a shared ENV variable for easier
updating.

Signed-off-by: Jean-Marc Valin <jmvalin@jmvalin.ca>

Author: rillian

.github/workflows/cmake.yml

@@ -2,6 +2,9 @@ name: CMake
 
 on: [push, pull_request]
 
+env:
+  NDK_VERSION: 27.2.12479018
+
 jobs:
   CMakeVersionTest:
     name: Test build with CMake 3.16.0
@@ -62,26 +65,26 @@ jobs:
             name: "Android/So/ARMv8/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a -DBUILD_SHARED_LIBS=ON"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a -DBUILD_SHARED_LIBS=ON"
           }
         # TODO: Android ARMv7
         # - {
         #     name: "Android/So/ARMv7/Release",
         #     os: ubuntu-latest,
         #     config: Release,
-        #     args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=armeabi-v7a -DBUILD_SHARED_LIBS=ON"
+        #     args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=armeabi-v7a -DBUILD_SHARED_LIBS=ON"
         #   }
         - {
             name: "Android/So/X86/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86 -DBUILD_SHARED_LIBS=ON"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86 -DBUILD_SHARED_LIBS=ON"
           }
         - {
             name: "Android/So/X64/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86_64 -DBUILD_SHARED_LIBS=ON"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86_64 -DBUILD_SHARED_LIBS=ON"
           }
         - {
             name: "Windows/Dll/X86/Release",
@@ -174,26 +177,26 @@ jobs:
             name: "Android/Lib/ARMv8/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=arm64-v8a"
           }
         # TODO: Android ARMv7
         # - {
         #     name: "Android/Lib/ARMv7/Release",
         #     os: ubuntu-latest,
         #     config: Release,
-        #     args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=armeabi-v7a"
+        #     args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=armeabi-v7a"
         #   }
         - {
             name: "Android/Lib/X86/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86"
           }
         - {
             name: "Android/Lib/X64/Release",
             os: ubuntu-latest,
             config: Release,
-            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/25.2.9519653/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86_64"
+            args: "-DCMAKE_TOOLCHAIN_FILE=${ANDROID_HOME}/ndk/${NDK_VERSION}/build/cmake/android.toolchain.cmake -DANDROID_ABI=x86_64"
           }
         - {
             name: "CustomModes/Linux/Lib/X64/Release",