RFR: 8306849: Missing headful in java/awt/Graphics/GetGraphicsTest.java

[Jie Fu]

Add `@key headful` in the test.

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Commit messages:
 - 8306849: Missing headful in java/awt/Graphics/GetGraphicsTest.java

Changes: https://git.openjdk.org/jdk/pull/13640/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13640&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306849
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13640.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13640/head:pull/13640

PR: https://git.openjdk.org/jdk/pull/13640