[configparser] Fix return type of RawConfigParser.read

[LeonDeKunlun]

No description provided.

[srittau]

We should use overloads here instead of returning a hard-to-handle list[str | bytes] type indiscriminately.

[github-actions]

Diff from mypy_primer, showing the effect of this PR on open source code:

meson (https://github.com/mesonbuild/meson)
+ mesonbuild/cmdline.py:46:5: error: Signature of "read" incompatible with supertype "configparser.RawConfigParser"  [override]
+ mesonbuild/cmdline.py:46:5: note:      Superclass:
+ mesonbuild/cmdline.py:46:5: note:          @overload
+ mesonbuild/cmdline.py:46:5: note:          def [AnyStr: (str, bytes)] read(self, filenames: AnyStr | PathLike[AnyStr], encoding: str = ...) -> list[AnyStr]
+ mesonbuild/cmdline.py:46:5: note:          @overload
+ mesonbuild/cmdline.py:46:5: note:          def read(self, filenames: Iterable[str | PathLike[str]], encoding: str | None = ...) -> list[str]
+ mesonbuild/cmdline.py:46:5: note:          @overload
+ mesonbuild/cmdline.py:46:5: note:          def read(self, filenames: Iterable[bytes | PathLike[bytes]], encoding: str | None = ...) -> list[bytes]
+ mesonbuild/cmdline.py:46:5: note:          @overload
+ mesonbuild/cmdline.py:46:5: note:          def read(self, filenames: Iterable[str | bytes | PathLike[str] | PathLike[bytes]], encoding: str | None = ...) -> list[str | bytes]
+ mesonbuild/cmdline.py:46:5: note:      Subclass:
+ mesonbuild/cmdline.py:46:5: note:          def read(self, filenames: str | bytes | PathLike[str] | PathLike[bytes] | Iterable[str | bytes | PathLike[str] | PathLike[bytes]], encoding: str | None = ...) -> list[str]
+ mesonbuild/cmdline.py:47:29: error: Argument 1 to "read" of "RawConfigParser" has incompatible type "str | bytes | PathLike[str] | PathLike[bytes] | Iterable[str | bytes | PathLike[str] | PathLike[bytes]]"; expected "str | PathLike[str]"  [arg-type]