checks: correct the shebang line filtering for python files
As it is, the only related file is docs/test2rst.py, which was covered by **.py.
Not sure if it matters, but most patterns in core tests are for "#!.*?python".
(Though there are a couple "#!.*python" tests.)
#require test-repo
$ checkflake8() {
> if ! (which flake8 > /dev/null); then
> echo skipped: missing tool: flake8;
> exit 80;
> fi;
> };
$ checkflake8
Copied from Mercurial core (60ee2593a270)
$ cd "`dirname "$TESTDIR"`"
run flake8 if it exists; if it doesn't, then just skip
$ hg files -0 'set:(**.py or grep("^#!.*python")) - removed()' 2>/dev/null \
> | xargs -0 flake8