typing: simplify archive.gz writing and drop a few pytype suppressions I was waiting until 3.8 to use `Literal` to fix this, but there's also the ":" and "|" characters that are passed along here, meant only for the non-gz archive types. But manipulating what the local caller passes is silly- we know we're writing, so just open it for writing. As an added bonus, PyCharm stops flagging the call too (since it doesn't know about pytype suppression comments).