ci: downgrade Java version from 23 to 21 in build configuration

.github/workflows/build.yml

@@ -69,7 +69,7 @@ jobs:
       - name: Build packets
         run: ./gradlew :libraries:packets:shadowJar
 
-  tests:
+  unit-tests:
     runs-on: ubuntu-latest
 
     steps:
@@ -88,7 +88,7 @@ jobs:
         uses: actions/setup-java@v2
         with:
           distribution: 'adopt'
-          java-version: '23'
+          java-version: '21'
 
       - name: Modify gradlew permissions
         run: chmod +x ./gradlew

tools/deployment/build.gradle.kts

@@ -8,7 +8,7 @@ group = "de.oliver"
 description = "Tool to deploy Minecraft plugins"
 
 java {
-    toolchain.languageVersion.set(JavaLanguageVersion.of(23))
+    toolchain.languageVersion.set(JavaLanguageVersion.of(21))
 }
 
 repositories {
@@ -42,7 +42,7 @@ tasks {
 
         // Set the release flag. This configures what version bytecode the compiler will emit, as well as what JDK APIs are usable.
         // See https://openjdk.java.net/jeps/247 for more information.
-        options.release.set(23)
+        options.release.set(21)
     }
 
     java {