Fix CI & update to java 21. (#247)

Author: jdijt

.github/workflows/ci.yml

@@ -21,8 +21,10 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: 'adopt'
-          java-version: '17'
+          java-version: '21'
 
+      - uses: sbt/setup-sbt@v1
+      
       - name: test coverage
         run: sbt qa
 
@@ -42,7 +44,9 @@ jobs:
         uses: actions/setup-java@v4
         with:
           distribution: 'adopt'
-          java-version: '17'
+          java-version: '21'
+
+      - uses: sbt/setup-sbt@v1
 
       - name: styleCheck
         run: sbt styleCheck

.gitignore

@@ -1,3 +1,4 @@
 target/
 .idea/
 .bsp/
+.vscode/