Run Java workflows on JDK 21

Closes #77.

Author: Philip Z

.github/workflows/ci.yml

@@ -15,7 +15,7 @@ jobs:
       - name: Set up JDK 17
         uses: actions/setup-java@v4
         with:
-          java-version: '17'
+          java-version: '21'
           distribution: 'temurin'
           cache: maven
       - name: Build with Maven

.github/workflows/release.yml

@@ -21,7 +21,7 @@ jobs:
       - uses: actions/setup-java@v5
         with:
           distribution: temurin
-          java-version: "17"
+          java-version: "21"
           cache: maven
           server-id: TEAQL
           server-username: TEAQL_MAVEN_USERNAME