[Bug] apache cloudberry gpbackup 2.1.0

### Apache Cloudberry version

I am getting the below error when trying to take schema level backups from a apache cloudberry 2.0 database and I am taking one schema after the other using gpbackup 2.1.0 utility from a bash script. Also I am using parallelism as 3

Note: I recently build the apache cloudberry 2.1.0 gpbackup utility from the source code --> https://cloudberry.apache.org/releases/#releases

[CRITICAL]:-A backup with timestamp 20260502005451 is already in progress. Wait 1 second and try the backup again.

[INFO]:-Beginning cleanup

[WARNING]:-Encountered error during cleanup: runtime error: invalid memory address or nil pointer dereference

[INFO]:-Cleanup complete

github.com/apache/cloudberry-backup/backup.createBackupLockFile
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/backup/wrappers.go:187
github.com/apache/cloudberry-backup/backup.DoSetup
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/backup/backup.go:51
main.main.func1
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/gpbackup.go:31
github.com/spf13/cobra.(*Command).execute
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/vendor/github.com/spf13/cobra/command.go:920
github.com/spf13/cobra.(*Command).ExecuteC
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/vendor/github.com/spf13/cobra/command.go:1044
github.com/spf13/cobra.(*Command).Execute
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/vendor/github.com/spf13/cobra/command.go:968
main.main
/home/test/cb_2_1/apache-cloudberry-backup-2.1.0/gpbackup.go:39
runtime.main
/usr/lib/golang/src/runtime/proc.go:285
runtime.goexit
/usr/lib/golang/src/runtime/asm_amd64.s:1693

Can you please kindly suggest the fix for the gpbackup 2.1.0

### What happened

[CRITICAL]:-A backup with timestamp 20260502005451 is already in progress. Wait 1 second and try the backup again.

[INFO]:-Beginning cleanup

[WARNING]:-Encountered error during cleanup: runtime error: invalid memory address or nil pointer dereference

[INFO]:-Cleanup complete

### What you think should happen instead

_No response_

### How to reproduce

Please kindly use the gpbackup utility version 2.1.0 with parallelism 3 and compression 2

### Operating System

OEL 9.7

### Anything else

_No response_

### Are you willing to submit PR?

- [ ] Yes, I am willing to submit a PR!

### Code of Conduct

- [x] I agree to follow this project's [Code of Conduct](https://github.com/apache/cloudberry/blob/main/CODE_OF_CONDUCT.md).

Start by reproducing gpbackup 2.1.0 against an Apache Cloudberry 2.0 database with parallelism 3 and compression 2. Trace the reported failure from backup/wrappers.go:187 through backup/backup.go:51 and gpbackup.go:31. Done should be demonstrated by schema-level backups no longer producing the lock error followed by the nil-pointer cleanup warning.

Written by the indexing model from the issue text.