Do not set last_enrolled_at when re-enrolling orbit (#20620)

Server fix for #20397. (I incorrectly added that `last_enrolled_at =
NOW()` on the first iOS/iPadOS support PR.)

- [X] Changes file added for user-visible changes in `changes/`,
`orbit/changes/` or `ee/fleetd-chrome/changes`.
See [Changes
files](https://fleetdm.com/docs/contributing/committing-changes#changes-files)
for more information.
- [x] Added/updated tests.
- [ ] Manual QA for all new/changed functionality.

changes/20397-do-not-set-last_enrolled_at-when-enrolling-orbit

@@ -0,0 +1 @@
+* Fixed a bug that set `last_enrolled_at` during orbit re-enrollment, which caused osquery enroll failures when `FLEET_OSQUERY_ENROLL_COOLDOWN` is set .

server/datastore/mysql/hosts.go

@@ -1874,7 +1874,6 @@ func (ds *Datastore) EnrollOrbit(ctx context.Context, isMDMEnabled bool, hostInf
         uuid = COALESCE(NULLIF(uuid, ''), ?),
         osquery_host_id = COALESCE(NULLIF(osquery_host_id, ''), ?),
         hardware_serial = COALESCE(NULLIF(hardware_serial, ''), ?),
-		last_enrolled_at = NOW(),
         team_id = ?
       WHERE id = ?`
 			_, err := tx.ExecContext(ctx, sqlUpdate,

server/datastore/mysql/hosts_test.go

@@ -8258,7 +8258,9 @@ func testHostsEnrollOrbit(t *testing.T, ds *Datastore) {
 		require.NoError(t, err)
 		h2OrbitFetched, err := ds.Host(ctx, h2Orbit.ID)
 		require.NoError(t, err)
-		require.NotEqual(t, h1OsqueryFetched.LastEnrolledAt, h2OrbitFetched.LastEnrolledAt)
+		// orbit should not update last_enrolled_at if re-enrolling (because last_enrolled_at
+		// is to be set by osquery only).
+		require.Equal(t, h1OsqueryFetched.LastEnrolledAt, h2OrbitFetched.LastEnrolledAt)
 		time.Sleep(1 * time.Second) // to test the update of last_enrolled_at
 		h2Osquery, err := ds.EnrollHost(ctx, false, dupUUID, dupUUID, dupHWSerial, uuid.New().String(), nil, 0)
 		require.NoError(t, err)