cmd/go/internal/modfetch: add Unlock before return in checkModSum
In cmd/go/internal/modfetch/fetch.go,
`checkModSum()` forgets Unlock before return, which may lead to deadlock.
https://github.com/golang/go/blob/
876c1feb7d5e10a6ff831de9db19b9ff0ea92fa8/src/cmd/go/internal/modfetch/fetch.go#L514-L520
The fix is to add `goSum.mu.Unlock()` before return.
Change-Id: I855b1c1bc00aeada2c1e84aabb5328f02823007d
GitHub-Last-Rev:
afeb3763dd1d08c4c15c4c4183fd5705da60dc4c
GitHub-Pull-Request: golang/go#38563
Reviewed-on: https://go-review.googlesource.com/c/go/+/229219
Run-TryBot: Jay Conrod <jayconrod@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Jay Conrod <jayconrod@google.com>