Fix failing migration by conditionally deleting old constraint (#33878)

<!-- Add the related story/sub-task/bug number, like Resolves #123, or
remove if NA -->
**Related issue:** Resolves #33876 

Modifies the migration to check for the old constraint before deleting
it in case it was created on mysql 5.7

No changes file since this is an unreleased bug

# Checklist for submitter

If some of the following don't apply, delete the relevant line.

- [x] Input data is properly validated, `SELECT *` is avoided, SQL
injection is prevented (using placeholders for values in statements)

## Testing

- [x] Added/updated automated tests
- [x] Where appropriate, [automated tests simulate multiple hosts and
test for host
isolation](https://github.com/fleetdm/fleet/blob/main/docs/Contributing/reference/patterns-backend.md#unit-testing)
(updates to one hosts's records do not affect another)

- [x] QA'd all new/changed functionality manually

For unreleased bug fixes in a release candidate, one of:

- [x] Confirmed that the fix is not expected to adversely impact load
test results

## Database migrations

- [x] Checked table schema to confirm autoupdate
- [x] Checked schema for all modified table for columns that will
auto-update timestamps during migration.
- [x] Confirmed that updating the timestamps is acceptable, and will not
cause unwanted side effects.
- [x] Ensured the correct collation is explicitly set for character
columns (`COLLATE utf8mb4_unicode_ci`).

server/datastore/mysql/migrations/tables/20250922083056_AddTableMDMAndroidProfiles.go

@@ -127,7 +127,6 @@ ALTER TABLE mdm_configuration_profile_labels
   ADD COLUMN android_profile_uuid VARCHAR(37) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL,
   ADD FOREIGN KEY (android_profile_uuid) REFERENCES mdm_android_configuration_profiles(profile_uuid) ON DELETE CASCADE,
   ADD UNIQUE KEY idx_mdm_configuration_profile_labels_android_label_name (android_profile_uuid, label_name),
-  DROP CONSTRAINT ck_mdm_configuration_profile_labels_apple_or_windows,
   -- only one of apple, android or windows profile uuid must be set
   ADD CONSTRAINT ck_mdm_configuration_profile_labels_profile_uuid
     CHECK (IF(ISNULL(apple_profile_uuid), 0, 1) + IF(ISNULL(windows_profile_uuid), 0, 1) + IF(ISNULL(android_profile_uuid), 0, 1) = 1)
@@ -136,6 +135,27 @@ ALTER TABLE mdm_configuration_profile_labels
 		return fmt.Errorf("alter mdm_configuration_profile_labels table: %w", err)
 	}
 
+	// our mysql version at the time this constraint was added did not support CHECK constraints so this may or may not exist for us
+	// to delete, so we create the new wider constraint above then, optionally, delete the older narrow one
+	checkIfOldConstraintExists := `
+	SELECT COUNT(*)
+	FROM INFORMATION_SCHEMA.TABLE_CONSTRAINTS
+	WHERE CONSTRAINT_SCHEMA = DATABASE() AND CONSTRAINT_TYPE = 'CHECK' AND TABLE_NAME = 'mdm_configuration_profile_labels'
+	AND CONSTRAINT_NAME = 'ck_mdm_configuration_profile_labels_apple_or_windows'`
+	var constraintCount int
+	if err := tx.QueryRow(checkIfOldConstraintExists).Scan(&constraintCount); err != nil {
+		return fmt.Errorf("check for old CHECK constraint on mdm_configuration_profile_labels: %w", err)
+	}
+	if constraintCount > 0 {
+		dropOldConstraint := `
+			ALTER TABLE mdm_configuration_profile_labels
+			DROP CONSTRAINT ck_mdm_configuration_profile_labels_apple_or_windows
+		`
+		if _, err := tx.Exec(dropOldConstraint); err != nil {
+			return fmt.Errorf("drop old CHECK constraint on mdm_configuration_profile_labels: %w", err)
+		}
+	}
+
 	alterAndroidDevicesTable := `
 ALTER TABLE android_devices
 	ADD COLUMN applied_policy_id VARCHAR(100) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci DEFAULT NULL,

server/datastore/mysql/migrations/tables/20250922083056_AddTableMDMAndroidProfiles_test.go

@@ -104,3 +104,11 @@ func TestUp_20250922083056(t *testing.T) {
 	// empty android host got updated, non-empty stayed the same, mac host not updated
 	require.Equal(t, []string{"from-enterprise", "got-one", ""}, got)
 }
+
+func TestUp_20250922083056_checkconstraint_missing(t *testing.T) {
+	// Create a DB without the old apple-or-windows constraint and verify the migration does not error
+	db := applyUpToPrev(t)
+	_, err := db.Exec(`ALTER TABLE mdm_configuration_profile_labels DROP CONSTRAINT ck_mdm_configuration_profile_labels_apple_or_windows`)
+	require.NoError(t, err)
+	applyNext(t, db)
+}