Merge bitcoin/bitcoin#26591: [24.x] ci: Skip COMMIT_RANGE if no CIRRUS_PR

fad1c55301 lint: Skip COMMIT_RANGE if no CIRRUS_PR (MarcoFalke)

Pull request description:

  Identical commit from https://github.com/bitcoin/bitcoin/pull/26588

  Untested, but this may fix the red-ness in https://cirrus-ci.com/github/bitcoin/bitcoin/24.x, e.g. https://cirrus-ci.com/task/4697153604419584:

  Backport requested in https://github.com/bitcoin/bitcoin/pull/26588#issuecomment-1328916876

ACKs for top commit:
  hebasto:
    ACK fad1c55301, the same commit as in #26588.

Tree-SHA512: 8d8a735e25bc1f774f8cbf058b95b7019941138ab78fb7819852755c7a416a783ee116457b97031d447639002353d7bf12ee8445275b7b5eec4abc7421cc171d

test/lint/lint-git-commit-check.py

@@ -46,6 +46,8 @@ def main():
             commit_range = merge_base + "..HEAD"
     else:
         commit_range = os.getenv("COMMIT_RANGE")
+        if commit_range == "SKIP_EMPTY_NOT_A_PR":
+            sys.exit(0)
 
     commit_hashes = check_output(["git", "log", commit_range, "--format=%H"], universal_newlines=True, encoding="utf8").splitlines()
 

test/lint/lint-whitespace.py

@@ -97,6 +97,8 @@ def main():
             commit_range = merge_base + "..HEAD"
     else:
         commit_range = os.getenv("COMMIT_RANGE")
+        if commit_range == "SKIP_EMPTY_NOT_A_PR":
+            sys.exit(0)
 
     whitespace_selection = []
     tab_selection = []