Bumps up CI JDK version to 21

Author: ndegwamartin

.github/workflows/codecov.yml

@@ -8,10 +8,10 @@ jobs:
     steps:
     - name: Checkout
       uses: actions/checkout@v4
-    - name: Set up JDK 17
+    - name: Set up JDK 21
       uses: actions/setup-java@v1
       with:
-        java-version: 17
+        java-version: 21
     - name: Install dependencies
       run: mvn install -DskipTests=true -Dmaven.javadoc.skip=true -B -V
     - name: Run tests and collect coverage
@@ -21,4 +21,4 @@ jobs:
       env:
         # To find this token, and how it is stored in the repo, see:
         # https://docs.codecov.com/docs/adding-the-codecov-token
-        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+        CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}