github-merge.py fails when log.showSignature true is set

[fanquake]

Due to:

bitcoin-maintainer-tools/github-merge.py

Line 349 in a65a970

assert len(head_commit) == 40

[laanwj]

I wonder if there's a way to reduce the script's dependency on specific git settings having a certain value.

That said, the most straightforward fix is to make it another thing overridden on the command line when calling the appropriate commands.