GHA: paths-ignore doesn't work

[KrisThielemans]

We currently try to disable runs if a commit only has files which don't affect the run

SIRF/.github/workflows/build-test.yml

Lines 4 to 19 in a31f2d2

	push:
	branches: [ master ]
	paths-ignore:
	- '**.md'
	- LICENSE.txt
	- NOTICE.txt
	- .mailmap
	- CITATION.cff
	pull_request:
	branches: [ master ]
	paths-ignore:
	- '**.md'
	- LICENSE.txt
	- NOTICE.txt
	- .mailmap
	- CITATION.cff

However, this isn't working. See e.g. #1157 with @ckolbPTB 's 911fa9e only affecting CHANGES.md but still triggering a job.