Update build-toolchain.yml for 5.6 release branch

Author: MaxDesiatov

.github/workflows/build-toolchain.yml

@@ -7,17 +7,19 @@ on:
       - swiftwasm-release/5.3
       - swiftwasm-release/5.4
       - swiftwasm-release/5.5
+      - swiftwasm-release/5.6
   pull_request:
     branches:
       - swiftwasm
       - swiftwasm-release/5.3
       - swiftwasm-release/5.4
       - swiftwasm-release/5.5
+      - swiftwasm-release/5.6
 jobs:
   build_toolchain:
     env:
       TOOLCHAIN_CHANNEL: DEVELOPMENT
-      DEVELOPER_DIR: /Applications/Xcode_13.0.app/Contents/Developer/
+      DEVELOPER_DIR: /Applications/Xcode_13.1.app/Contents/Developer/
     strategy:
       matrix:
         include: