Bump the JVM toolchain version to 11

The error message from the GitHub Actions workflow of commit 1e4a711:
```text
> Could not resolve all files for configuration ':buildSrc:compileClasspath'.
   > Could not resolve com.android.tools.build:gradle:8.5.2.
     Required by:
         project :buildSrc
      > Dependency requires at least JVM runtime version 11. This build uses a Java 8 JVM.
```

buildSrc/src/main/kotlin/common-conventions.gradle.kts

@@ -21,7 +21,7 @@ kotlin {
     // for `androidx.compose`
 
     jvm() // TODO: `jvm("desktop")`?
-    jvmToolchain(8)
+    jvmToolchain(11)
 
     //androidTarget()