Use GObject type checking for instance arguments

Add a g_type_is_a check to interface/object instance arguments in addition
to the Python IsInstance check. This loosens restrictions on overrides which
don't use gi.overrides.override() and is needed to keep API compatibility
which broke with commit:
https://git.gnome.org/browse/pygobject/commit/?id=d5925b76

https://bugzilla.gnome.org/show_bug.cgi?id=724009
release 3.11.90
configure.ac: post release version bump to 3.11.91
Update release steps to be more explicit in regards to NEWS

Add an explicit step to commit the NEWS changes and push prior tagging.
Fix Build on Visual Studio

Some items from pygi-enum-marshal.c were moved to pygi-basictype.c, which
included the use of the NAN and INFINITY macros/constants, so the
definitions for those need to be moved to pygi-basictype.c as well.  Also
avoid defining a variable in the middle of the block.

https://bugzilla.gnome.org/show_bug.cgi?id=725122