RFR: 8356053: Test java/awt/Toolkit/Headless/HeadlessToolkit.java fails by timeout

[Sergey Bylokhov]

The `java/awt/Toolkit/Headless/HeadlessToolkit.java` test covers some functionality of various methods in the `HeadlessToolkit` class, specifically whether these methods throw a `HeadlessException` or not. The image-related methods do not require access to a remote server via a URL; they can be tested using a URL pointing to a local file. This ensures that the test does not depend on `openjdk.org`.

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Commit messages:
 - 8356053: Test java/awt/Toolkit/Headless/HeadlessToolkit.java fails by timeout

Changes: https://git.openjdk.org/jdk/pull/25045/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25045&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8356053
  Stats: 26 lines in 1 file changed: 15 ins; 4 del; 7 mod
  Patch: https://git.openjdk.org/jdk/pull/25045.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25045/head:pull/25045

PR: https://git.openjdk.org/jdk/pull/25045