chore: add comments for "api/healthz", clean up test env (#36481)

GITEA_UNIT_TESTS_LOG_SQL is renamed to GITEA_TEST_LOG_SQL

cmd/main.go

@@ -149,7 +149,7 @@ func NewMainApp(appVer AppVersion) *cli.Command {
 	app.Commands = append(app.Commands, subCmdWithConfig...)
 	app.Commands = append(app.Commands, subCmdStandalone...)
 
-	setting.InitGiteaEnvVars()
+	setting.UnsetUnnecessaryEnvVars()
 	return app
 }