[Java] Use Ubuntu 20.04 for most Linux builds excepts for CLang build that is using Ubuntu 18.04.

Author: vyazelenko

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ env:
 jobs:
   java-build:
     name: Java ${{ matrix.java }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
@@ -44,7 +44,7 @@ jobs:
 
   csharp-build:
     name: C# ${{ matrix.dotnet }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
@@ -87,7 +87,7 @@ jobs:
 
   cpp-gcc-build:
     name: C++ GCC ${{ matrix.version }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-20.04
     strategy:
       fail-fast: false
       matrix:
@@ -122,7 +122,7 @@ jobs:
 
   cpp-clang-build:
     name: C++ Clang ${{ matrix.version }}
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-18.04
     strategy:
       fail-fast: false
       matrix:
@@ -147,12 +147,10 @@ jobs:
           key: ${{ runner.os }}-gradle-wrapper-${{ hashFiles('**/gradle/wrapper/gradle-wrapper.properties') }}
       - name: Install compiler
         run: |
+          curl -L https://apt.llvm.org/llvm-snapshot.gpg.key | sudo apt-key add -
           sudo add-apt-repository "deb http://apt.llvm.org/bionic/ llvm-toolchain-bionic-${{ matrix.version }} main"
-
           sudo apt-get update
-
           sudo apt-get install -y clang-${{ matrix.version }} libsparsehash-dev
-
           curl -O -L https://github.com/Kitware/CMake/releases/download/v${CMAKE_VERSION}/cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz
           tar xf cmake-${CMAKE_VERSION}-Linux-x86_64.tar.gz
           echo "cmake-${CMAKE_VERSION}-Linux-x86_64/bin" >> $GITHUB_PATH