dist: Address Copilot review suggestions from PR #1042 (GraalVM Community) (#1059)

- installer: surface a clear error when the GraalVM Community releases
  listing is not a JSON array, instead of silently treating an error
  payload (rate limit, auth failure, etc.) as "no releases" which later
  surfaced as a misleading "version not found" error.
- docs: fix the GraalVM Community advanced-usage example to check the
  installed binary versions (java/native-image --version) rather than
  running a non-existent HelloWorldApp classpath that fails when copied.
- tests: cover the new non-array release listing error path.

Rebuilt dist bundle.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

docs/advanced-usage.md

@@ -186,8 +186,8 @@ steps:
     distribution: 'graalvm-community'
     java-version: '21'
 - run: |
-    java -cp java HelloWorldApp
-    native-image -cp java HelloWorldApp
+    java --version
+    native-image --version
 ```
 
 ### JetBrains