feat(readme): update Java version to 25 in setup examples (#969)

Updated the Java version in the README setup examples from 21 to 25
to reflect the latest supported version. This change ensures that
users are guided to use the most current Java version for their
projects.

- Updated all instances of 'java-version: 21' to 'java-version: 25'
- Modified supported version syntax to include '25'

README.md

@@ -82,7 +82,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin' # See 'Supported distributions' for available options
-    java-version: '21'
+    java-version: '25'
 - run: java HelloWorldApp.java
 ```
 
@@ -93,13 +93,13 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'zulu' # See 'Supported distributions' for available options
-    java-version: '21'
+    java-version: '25'
 - run: java HelloWorldApp.java
 ```
 
 #### Supported version syntax
 The `java-version` input supports an exact version or a version range using [SemVer](https://semver.org/) notation:
-- major versions: `8`, `11`, `16`, `17`, `21`
+- major versions: `8`, `11`, `16`, `17`, `21`, `25`
 - more specific versions: `8.0.282+8`, `8.0.232`, `11.0`, `11.0.4`, `17.0`
 - early access (EA) versions: `15-ea`, `15.0.0-ea`
 
@@ -149,7 +149,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin'
-    java-version: '21'
+    java-version: '25'
     cache: 'gradle'
     cache-dependency-path: | # optional
       sub-project/*.gradle*
@@ -169,7 +169,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin'
-    java-version: '21'
+    java-version: '25'
     cache: 'maven'
     cache-dependency-path: 'sub-project/pom.xml' # optional
 - name: Build with Maven
@@ -183,7 +183,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin'
-    java-version: '21'
+    java-version: '25'
     cache: 'sbt'
     cache-dependency-path: | # optional
       sub-project/build.sbt
@@ -203,7 +203,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin'
-    java-version: '21'
+    java-version: '25'
     cache: 'gradle'
 - run: ./gradlew build --no-daemon
 ```
@@ -223,7 +223,7 @@ steps:
 - uses: actions/setup-java@v5
   with:
     distribution: 'temurin'
-    java-version: '21'
+    java-version: '25'
     check-latest: true
 - run: java HelloWorldApp.java
 ```
@@ -235,7 +235,7 @@ jobs:
     runs-on: ubuntu-20.04
     strategy:
       matrix:
-        java: [ '8', '11', '17', '21' ]
+        java: [ '8', '11', '17', '21', '25' ]
     name: Java ${{ matrix.Java }} sample
     steps:
       - uses: actions/checkout@v6