RFR: CODETOOLS-7903246: Use homebrew/bin for pandoc if available

[Jonathan Gibbons]

Please review a simple patch to include `/opt/homebrew/bin` in the list of locations to look for pandoc.

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Commit messages:
 - CODETOOLS-7903246: Use homebrew/bin for pandoc if available

Changes: https://git.openjdk.org/jtreg/pull/100/files
 Webrev: https://webrevs.openjdk.org/?repo=jtreg&pr=100&range=00
  Issue: https://bugs.openjdk.org/browse/CODETOOLS-7903246
  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jtreg/pull/100.diff
  Fetch: git fetch https://git.openjdk.org/jtreg pull/100/head:pull/100

PR: https://git.openjdk.org/jtreg/pull/100