[4.6.x] Fix one issue for compat::getfuncargnames

[SeanXu1984]

Fix so the self of an instancemethod will not be removed again in getfuncargnames because it is already removed from signature(function)

I will deal with changelog later.

[SeanXu1984]

@nicoddemus I don't think the CI failure was introduced by my change. Could you help me with this please?

[RonnyPfannschmidt]

Travis seems to fail with tmpdir cleanup

[bluetech]

I've edited the title to add [4.6.x] since it targets that branch.

[Zac-HD]

@SeanXu1984 - it looks like this issue also affects the master branch. Could you please

1. Describe the problem that this patch fixes? Ideally by adding a test that failed before and passes now, but a prose description would also be OK.
2. Open a pull request targeting the master branch instead; we can backport it to 4.6 after merging.

[RonnyPfannschmidt]

as far as i can tell this one tries to add bound methods, which is not something pytest itself collects

we need a accompanying unit-test at least and a reference for the usage, else its bound to cause confusion later on

also in order to be integrated properly we need it as feature in master and do a back-port later on

[SeanXu1984]

I've created another PR for main branch. #6882

[nicoddemus]

Closing for now as in #6882. 👍