git-codereview: do not require gofmt for testdata files

We use Go files as testdata for gopls, specifically as test cases for
formatting and imports.

Change-Id: Ie4ed6097960eb0eb3d5c1767b8b76bed147c81e0
Reviewed-on: https://go-review.googlesource.com/c/review/+/173339
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
diff --git a/git-codereview/gofmt.go b/git-codereview/gofmt.go
index 12ea801..f47c43d 100644
--- a/git-codereview/gofmt.go
+++ b/git-codereview/gofmt.go
@@ -348,6 +348,9 @@
 	if strings.HasPrefix(file, "vendor/") || strings.Contains(file, "/vendor/") {
 		return false
 	}
+	if strings.HasPrefix(file, "testdata/") || strings.Contains(file, "/testdata/") {
+		return false
+	}
 	if !strings.HasPrefix(file, "test/") {
 		return true
 	}