test: Fix flaky receive/multitsdb test

[cincinnat]

There is race condition in TestMultiTSDBPrune due to a dangling goroutine which can fail outside of the test function's lifetime if the database object is closed before Sync() is finished.

• I added CHANGELOG entry for this change.
• Change is not relevant to the end user.

Changes

Verification

Can be reliably reproduced with a simple change:

--- a/pkg/receive/multitsdb_test.go
+++ b/pkg/receive/multitsdb_test.go
@@ -502,6 +502,7 @@ func syncTSDBs(ctx context.Context, m *MultiTSDB, interval time.Duration) error
                case <-ctx.Done():
                        return nil
                case <-time.After(interval):
+                       time.Sleep(100 * time.Millisecond)
                        _, err := m.Sync(ctx)
                        if err != nil {
                                return err

[pedro-stanaka]

lgtm - ty

[fpetkovski]

Thanks