Replace remaining calls to testing.Short where possible. (#110765)

* Replace remaining calls to testing.Short where possible.
* Update style guide.
* Revert change in TestAlertmanager_ExtraDedupStage, as it doesn't work.
* Make TestAlertRulePostExport into integration test.

pkg/tests/alertmanager/alertmanager_test.go

@@ -8,6 +8,7 @@ import (
 )
 
 func TestAlertmanager_ExtraDedupStage(t *testing.T) {
+	// TODO: rename test and call testutil.SkipIntegrationTestInShortMode(t)
 	if testing.Short() {
 		t.Skip("skipping integration test")
 	}