<AWT Dev> RFR: 8261368: The new TestNullSetColor test is placed in the wrong group

[Sergey Bylokhov]

The test is moved to the "java/awt/Graphics/" since it validates behavior of the java.awt.Graphics$setColor() method.

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Commit messages:
 - Update TestNullSetColor.java

Changes: https://git.openjdk.java.net/jdk/pull/2467/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2467&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8261368
  Stats: 0 lines in 1 file changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2467.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2467/head:pull/2467

PR: https://git.openjdk.java.net/jdk/pull/2467