internal: fix struct field name in comment

Change-Id: I45d8f020fec48cf099b7703edfa0f85944cdc7f5
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/805821
kokoro-CI: kokoro <noreply+kokoro@google.com>
LUCI-TryBot-Result: golang-scoped@luci-project-accounts.iam.gserviceaccount.com <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Hyang-Ah Hana Kim <hyangah@gmail.com>
Reviewed-by: Ethan Lee <ethanalee@google.com>

Author: cuishuang

internal/datasource.go

@@ -153,7 +153,7 @@ type TestingDataSource interface {
 	// It calls t.Fatal if there is an error.
 	MustInsertModule(t *testing.T, m *Module)
 
-	// MustInsertModule inserts m into the DataSource
+	// MustInsertModuleGoMod inserts m into the DataSource
 	// with a go.mod file.
 	// It calls t.Fatal if there is an error.
 	// TODO(jba); remove context arg.