dev: go-lint only looks for go.mod files

Created by: keegancsmith

We had "-type file" which broke since this doesn't work on linux. This was removed, but now we get a test directory called go.mod matching which is incorrect. This adds back the find condition, but correctly works on both mac and linux.

$ diff <(find . -name go.mod -type f) <(find . -name go.mod)
1a2
> ./internal/codeintel/dependencies/internal/lockfiles/testdata/parse/go.mod

Test Plan: ran the find incantation on both linux and mac. Both agreed and found all go.mod files.

Context: https://github.com/sourcegraph/sourcegraph/pull/34298/files#r855806408