RFR: 8375015: CompletionAPITest::testDocumentation failed - AssertionFailedError: expected: <null> but was: <jshelltest.JShellTest>

[Christian Stein]

Please review this change to allow the test do work on more machines.

Prior to this change, the timeout was too tight and the busy-waiting loop to CPU greedy (on some machines) to let the underlying garbarge collector perform its work and release the referene in question. That led to an assertion that failed.

This change increases the timeout by a flat 10x and also "yields" by invoking `Thread.sleep(100)` in the wait loop.

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Commit messages:
 - 8375015: CompletionAPITest::testDocumentation failed - AssertionFailedError: expected: <null> but was: <jshelltest.JShellTest>

Changes: https://git.openjdk.org/jdk/pull/29196/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=29196&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8375015
  Stats: 5 lines in 1 file changed: 1 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/29196.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/29196/head:pull/29196

PR: https://git.openjdk.org/jdk/pull/29196