feat(build.gradle): down-grade the java version from 21 to 17

app/build.gradle.kts

@@ -21,7 +21,7 @@ dependencies {
 // Apply a specific Java toolchain to ease working on different environments.
 java {
     toolchain {
-        languageVersion = JavaLanguageVersion.of(21)
+        languageVersion = JavaLanguageVersion.of(17)
     }
 }