cmd/go: include internal/godebugs in TestNewReleaseRebuildsStalePackagesInGOPATH

This fixes a lingering failure on the 'longtest' builders,
introduced in CL 476280.

For golang#57001.

Change-Id: I18872b1bc990dd16c0b86ebc5878c0a04ce9b2d9
Reviewed-on: https://go-review.googlesource.com/c/go/+/485897
Run-TryBot: Bryan Mills <[email protected]>
Commit-Queue: Bryan Mills <[email protected]>
Auto-Submit: Bryan Mills <[email protected]>
Reviewed-by: Michael Matloob <[email protected]>
TryBot-Result: Gopher Robot <[email protected]>

Author: Bryan C. Mills

src/cmd/go/go_test.go

@@ -899,6 +899,7 @@ func TestNewReleaseRebuildsStalePackagesInGOPATH(t *testing.T) {
 		"src/internal/coverage/rtcov",
 		"src/internal/cpu",
 		"src/internal/goarch",
+		"src/internal/godebugs",
 		"src/internal/goexperiment",
 		"src/internal/goos",
 		"src/internal/coverage/rtcov",