protosanitizer: test +v conversion

Sometimes "%+v" was used to print a message although it produces the
same output as "%v" and "%s" for gRPC messages because they implement
fmt.Stringer. It's worthwhile having a test that ensures that wrapping
the message with StripSecrets and printing with "+v" still works.

Author: pohly

protosanitizer/protosanitizer_test.go

@@ -210,7 +210,9 @@ func TestStripSecrets(t *testing.T) {
 			stripped = StripSecrets(c.original)
 		}
 		if assert.Equal(t, c.stripped, fmt.Sprintf("%s", stripped), "unexpected result for fmt s of %s", c.original) {
-			assert.Equal(t, c.stripped, fmt.Sprintf("%v", stripped), "unexpected result for fmt v of %s", c.original)
+			if assert.Equal(t, c.stripped, fmt.Sprintf("%v", stripped), "unexpected result for fmt v of %s", c.original) {
+				assert.Equal(t, c.stripped, fmt.Sprintf("%+v", stripped), "unexpected result for fmt +v of %s", c.original)
+			}
 		}
 		assert.Equal(t, before, fmt.Sprint(c.original), "original value modified")
 	}