Revert Java 25 toolchain back to Java 21 (#167)

* Revert "Use Java 25 toolchain going forward (#154)"

This reverts commit 3b44daf.

* Restore .claude/settings.local.json in .gitignore

Author: timtebeek

.github/workflows/ci.yml

@@ -32,7 +32,7 @@ jobs:
       - uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: 25
+          java-version: 21
       - uses: gradle/actions/setup-gradle@v5
       - name: build
         run: ./gradlew ${{ env.GRADLE_SWITCHES }} build

.github/workflows/publish.yml

@@ -20,7 +20,7 @@ jobs:
       - uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: 25
+          java-version: 21
 
       - uses: gradle/actions/setup-gradle@v5
       - name: publish-candidate

src/main/java/org/openrewrite/gradle/RewriteJavaPlugin.java

@@ -58,7 +58,7 @@ public void apply(Project project) {
         });
 
         project.getExtensions().configure(JavaPluginExtension.class, java ->
-                java.toolchain(toolchain -> toolchain.getLanguageVersion().set(JavaLanguageVersion.of(25))));
+                java.toolchain(toolchain -> toolchain.getLanguageVersion().set(JavaLanguageVersion.of(21))));
 
         project.getConfigurations().all(config -> config.resolutionStrategy(strategy ->
                 strategy.cacheDynamicVersionsFor(0, "seconds")));