The Go file changes didn't actually check the file extensions for the
files the Go extension is receiving. This error was not noticed because
the VSCode extension doesn't yet actually send mod files to gopls yet,
but it will in its next release.
Fixesgolang/go#32178
Change-Id: Ia04d0a92ce7df13fcf4c601421bc000d69855f6d
Reviewed-on: https://go-review.googlesource.com/c/tools/+/178679
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Ian Cottrell <iancottrell@google.com>