Copy-DbaDatabase - Pass IgnoreFileChecks to Backup-DbaDatabase for UNC paths

When xp_fileexist fails (e.g. due to certificate issues), Test-DbaPath returns
false. Copy-DbaDatabase already handles this gracefully with a "Trying anyway"
message, but then called Backup-DbaDatabase without -IgnoreFileChecks, causing
Backup-DbaDatabase to run its own Test-DbaPath check, fail, and abort.

Adding -IgnoreFileChecks to the non-Azure Backup-DbaDatabase calls skips the
redundant internal path check (Copy-DbaDatabase already validates paths) so the
backup proceeds when the SQL Server service account can actually access the path.

Fixes #10286

(do Copy-DbaDatabase)

Co-authored-by: Andreas Jordan <andreasjordan@users.noreply.github.com>

Author: github-actions[bot]

public/Copy-DbaDatabase.ps1

@@ -1239,10 +1239,18 @@ function Copy-DbaDatabase {
                                         }
 
                                     } else {
+                                        $splatBackup = @{
+                                            SqlInstance      = $sourceServer
+                                            Database         = $dbName
+                                            BackupDirectory  = $SharedPath
+                                            FileCount        = $numberfiles
+                                            CopyOnly         = $CopyOnly
+                                            IgnoreFileChecks = $true
+                                        }
                                         if ($AdvancedBackupParams) {
-                                            $backupTmpResult = Backup-DbaDatabase -SqlInstance $sourceServer -Database $dbName -BackupDirectory $SharedPath -FileCount $numberfiles -CopyOnly:$CopyOnly @AdvancedBackupParams
+                                            $backupTmpResult = Backup-DbaDatabase @splatBackup @AdvancedBackupParams
                                         } else {
-                                            $backupTmpResult = Backup-DbaDatabase -SqlInstance $sourceServer -Database $dbName -BackupDirectory $SharedPath -FileCount $numberfiles -CopyOnly:$CopyOnly
+                                            $backupTmpResult = Backup-DbaDatabase @splatBackup
                                         }
                                     }