RFR: CODETOOLS-7903222: update entries in .gitignore

[Jonathan Gibbons]

Please review some minor updates to .gitignore

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Commit messages:
 - CODETOOLS-7903222: update entries in .gitignore

Changes: https://git.openjdk.org/jtreg/pull/91/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=91&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903222
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jtreg/pull/91.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/91/head:pull/91

PR: https://git.openjdk.org/jtreg/pull/91