RFR: 8315960: test/jdk/java/io/File/TempDirDoesNotExist.java leaves test files behind

[Brian Burkhalter]

Add a `finally` block to delete the created files.

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Commit messages:
 - 8315960: test/jdk/java/io/File/TempDirDoesNotExist.java leaves test files behind

Changes: https://git.openjdk.org/jdk/pull/15757/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15757&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315960
  Stats: 14 lines in 1 file changed: 9 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/15757.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15757/head:pull/15757

PR: https://git.openjdk.org/jdk/pull/15757