[lworld] Integrated: GitHub actions ignore main project branches

[David Simms]

Ignore branches (when sync-ing in PF, causes extra work)

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Commit messages:
 - Syntax 4
 - Syntax 3
 - Syntax 2
 - Syntax 1
 - GH actions ignore main branches

Changes: https://git.openjdk.java.net/valhalla/pull/252/files
 Webrev: https://webrevs.openjdk.java.net/?repo=valhalla&pr=252&range=00
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/valhalla/pull/252.diff
  Fetch: git fetch https://git.openjdk.java.net/valhalla pull/252/head:pull/252

PR: https://git.openjdk.java.net/valhalla/pull/252