RFR: 8366439: test/jdk/java/util/zip/ZipFile/ZipSourceCache.java fails with AssertionFailedError: expected: <6> but was: <5>

[Jaikiran Pai]

Can I please get a review of this test-only change which addresses a failure in `test/jdk/java/util/zip/ZipFile/ZipSourceCache.java` test?

As noted in the description of https://bugs.openjdk.org/browse/JDK-8366439, this test fails if the underlying file system's timestamp granularity doesn't allow for the last modified timestamp to increase when the test's ZIP file is updated with newer content.

The change in this PR updates the test to first check that the last modified timestamp has increased on the ZIP file that was updated, before running the rest of the test assertions. The test continues to pass in our CI with this change.

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Commit messages:
 - 8366439: test/jdk/java/util/zip/ZipFile/ZipSourceCache.java fails with AssertionFailedError: expected: <6> but was: <5>

Changes: https://git.openjdk.org/jdk/pull/27005/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27005&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366439
  Stats: 16 lines in 1 file changed: 11 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27005.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27005/head:pull/27005

PR: https://git.openjdk.org/jdk/pull/27005