Bump workflows JDK to 21 (mihonapp/mihon#3053)

(cherry picked from commit ce5820b496dc6526b7afbf7344753c923802f737)

.github/.java-version

@@ -0,0 +1 @@
+21

.github/workflows/build_benchmark.yml

@@ -64,7 +64,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@1bcf9fb12cf4aa7d266a90ae39939e61372fe520 # v5.4.0
         with:
-          java-version: 17
+          java-version-file: .github/.java-version
           distribution: temurin
 
       - name: Set up gradle

.github/workflows/build_preview.yml

@@ -126,7 +126,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@1bcf9fb12cf4aa7d266a90ae39939e61372fe520 # v5.4.0
         with:
-          java-version: 17
+          java-version-file: .github/.java-version
           distribution: temurin
 
       - name: Write google-services.json

.github/workflows/build_pull_request.yml

@@ -43,7 +43,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@1bcf9fb12cf4aa7d266a90ae39939e61372fe520 # v5.4.0
         with:
-          java-version: 17
+          java-version-file: .github/.java-version
           distribution: temurin
 
       - name: Write google-services.json

.github/workflows/build_push.yml

@@ -34,7 +34,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@1bcf9fb12cf4aa7d266a90ae39939e61372fe520 # v5.4.0
         with:
-          java-version: 17
+          java-version-file: .github/.java-version
           distribution: temurin
 
       - name: Write google-services.json

.github/workflows/build_release.yml

@@ -94,7 +94,7 @@ jobs:
       - name: Set up JDK
         uses: actions/setup-java@1bcf9fb12cf4aa7d266a90ae39939e61372fe520 # v5.4.0
         with:
-          java-version: 17
+          java-version-file: .github/.java-version
           distribution: temurin
 
       - name: Write google-services.json