Clarify Bazel 8.0 is not yet supported (#1118) (#1123)

As Mozc is not compatible with Bazel 8.0 yet, let's

 * pin Bazel version to Bazel 7.4.1 in GitHub Actions.
 * clarify that Bazel 8.0 is not supported in the build instructions.

PiperOrigin-RevId: 698388242

.github/workflows/android.yaml

@@ -29,6 +29,8 @@ jobs:
 
       - name: build
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel build --config oss_android package --config release_build
 

.github/workflows/linux.yaml

@@ -33,6 +33,8 @@ jobs:
 
       - name: bazel build
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel build --config oss_linux package --config release_build
 
@@ -64,5 +66,7 @@ jobs:
 
       - name: bazel test
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel test ... --config oss_linux --build_tests_only -c dbg

.github/workflows/macos.yaml

@@ -54,6 +54,8 @@ jobs:
 
       - name: bazel build
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel build --config oss_macos package --macos_cpus=arm64 --config release_build
 
@@ -103,6 +105,8 @@ jobs:
 
       - name: bazel build
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel build --config oss_macos package --macos_cpus=x86_64 --config release_build
 
@@ -152,6 +156,8 @@ jobs:
 
       - name: bazel build
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel build --config oss_macos package --macos_cpus=x86_64,arm64 --config release_build
 
@@ -201,6 +207,8 @@ jobs:
 
       - name: bazel test
         working-directory: ./src
+        env:
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel test ... --config oss_macos --build_tests_only -c dbg
 

.github/workflows/windows.yaml

@@ -122,6 +122,7 @@ jobs:
         working-directory: .\src
         env:
           ANDROID_NDK_HOME: ""
+          USE_BAZEL_VERSION: "7.4.1"
         run: |
           bazel --bazelrc=windows.bazelrc build --config oss_windows --config release_build package