Fix attempt #4

Author: danslapman

.github/workflows/ci.yml

@@ -299,7 +299,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
           check-latest: true
 
       - uses: sbt/setup-sbt@v1
@@ -357,7 +357,7 @@ jobs:
       - uses: actions/setup-java@v4
         with:
           distribution: temurin
-          java-version: 17
+          java-version: 21
           check-latest: true
 
       - uses: sbt/setup-sbt@v1

backend/project/Settings.scala

@@ -41,7 +41,7 @@ object Settings {
       "-feature",
       "-language:higherKinds",
       "-language:implicitConversions",
-      "-release", "17", //https://github.com/scala/scala3/issues/20373
+      "-release", "21",
       "-unchecked",
       "-Xmax-inlines", "64",
       "-Ybackend-parallelism",