Fix TestGitOpsFullGlobal failing on main after Windows BatchSetMDMProfiles change (#48695)

Fixes `TestGitOpsFullGlobal`, which has been failing the `fleetctl` test
bundle on every `main` run since #48467 merged (bisected to a90eab6f62,
e.g. [this
run](https://github.com/fleetdm/fleet/actions/runs/28665588825)).

#48467 changed `BatchSetMDMProfiles` so that `assume_enabled` is only
honored on dry runs; real runs now validate Windows profiles against the
app config persisted in the datastore. That's correct in production,
because the GitOps run persists `windows_enabled_and_configured: true`
via `ModifyAppConfig` before the profiles batch call. But this test's
`AppConfigFunc` mock always returned a fixed app config with Windows MDM
disabled, never reflecting what `SaveAppConfigFunc` stored — so the
real-run profiles batch now fails with 422 "Windows MDM isn't turned
on".

The fix makes the mock behave like the real datastore: once
`SaveAppConfig` is called, `AppConfigFunc` returns the saved config.
Test-only change, no product code touched.

# Checklist for submitter

- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements), JS
inline code is prevented especially for url redirects, and untrusted
data interpolated into shell scripts/commands is validated against shell
metacharacters.
- [x] Timeouts are implemented and retries are limited to avoid infinite
loops

## Testing

- [x] Added/updated automated tests

`go test -run TestGitOps ./cmd/fleetctl/fleetctl/` passes locally (it
fails on `main` without this change).


<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

* **Tests**
* Improved GitOps test coverage to better match real persistence
behavior during an apply run.
* Updated test setup so saved app configuration is read back correctly
after changes are applied.
* Reset test state between subtests to keep each scenario isolated and
reliable.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

cmd/fleetctl/fleetctl/gitops_test.go

@@ -2158,11 +2158,20 @@ func TestGitOpsFullGlobal(t *testing.T) {
 	}
 
 	// App config
+	appConfigSaved := false
 	ds.AppConfigFunc = func(ctx context.Context) (*fleet.AppConfig, error) {
+		if appConfigSaved {
+			// Return the config persisted earlier in the same GitOps run, as the real
+			// datastore would: profile validation re-reads the app config after
+			// org_settings has enabled Windows MDM.
+			config := *savedAppConfig
+			return &config, nil
+		}
 		return &fleet.AppConfig{MDM: fleet.MDM{EnabledAndConfigured: true}}, nil
 	}
 	ds.SaveAppConfigFunc = func(ctx context.Context, config *fleet.AppConfig) error {
 		savedAppConfig = config
+		appConfigSaved = true
 		return nil
 	}
 	ds.IsEnrollSecretAvailableFunc = func(ctx context.Context, secret string, isNew bool, teamID *uint) (bool, error) {
@@ -2199,6 +2208,7 @@ func TestGitOpsFullGlobal(t *testing.T) {
 			deletedLabels = nil
 			enrolledSecrets = nil
 			savedAppConfig = &fleet.AppConfig{}
+			appConfigSaved = false
 			policyDeleted = false
 			queryDeleted = false
 			deletedPolicyIDs = nil