<Swing Dev> RFR: 8269269: [macos11] SystemIconTest fails with ClassCastException

[Alexander Zuev]

Do not test situation where UIResource icon is returned
Added a whole bunch of debug information to see what file test is filed
upon.

-------------

Commit messages:
 - 8269269: [macos11] SystemIconTest fails with ClassCastException

Changes: https://git.openjdk.java.net/jdk/pull/4776/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4776&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8269269
  Stats: 21 lines in 1 file changed: 13 ins; 4 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4776.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4776/head:pull/4776

PR: https://git.openjdk.java.net/jdk/pull/4776