Drop CPython 3.6 support

[yunline]

Issue: #1850

[Starbuck5]

@ankith26 What do you want to do about the ubuntu-18.04 build here?

[ankith26]

If we are dropping 3.6 we also have to drop the 18.04 build (gh actions have deprecated it anyways)

[MyreMylar]

LGTM 👍

I can't find any more CPython 3.6 references outside of a single comment (which is still relevant).

[MyreMylar]

Looking at > 3.7 stuff we could get rid of the blocks like this:

#if PY_VERSION_HEX < 0x03070000
#ifdef WITH_THREAD
    PyEval_InitThreads();
#endif /* WITH_THREAD */
#endif

Search for : 0x03070000 and there are two like this in rwobject.c and _pygame.h

[itzpr3d4t0r]

yeah the _pygame.h one should be related to the FASTCALL macros we introduced a while back for back compat with 3.6.

[MyreMylar]

Changes look good 👍

[oddbookworm]

LGTM! But seeing as how major a change this is, I'm not going to merge it because I think we might want at least one more approval?

[ankith26]

Overall the PR looks good, left two minor reviews for your consideration. You may choose to fix these in this PR, or (you or anyone else can) do a different PR shortly after merging this.

Thanks for the PR! 🎉