Changes

fix(ticdc): skip empty log archive in integration pipelines (#4162)

## Summary

- fix log collection in TiCDC integration pipelines when
`/tmp/tidb_cdc_test/` contains no `*.log`
- replace direct `tar ... $(find ... '*.log')` with a guarded flow:
  - collect log file list first
  - only run `tar` when list is non-empty
  - print a skip message when no logs are found
- apply the same behavior across:
  - `pipelines/pingcap/ticdc/latest/*`
  - `pipelines/pingcap/ticdc/latest/*_next_gen/*`
  - `pipelines/pingcap/ticdc/release-9.0-beta/*`

## Root Cause

When `find` returns an empty result, `tar` is called without input files
and exits with:

- `tar: Cowardly refusing to create an empty archive`
- exit code `2`

This causes the post-failure log collection step to fail unexpectedly.

## Testing

- reproduced old behavior locally: empty log directory + original `tar`
invocation returns exit code `2`
- verified new guarded snippet behavior:
  - no log files: step exits normally and prints skip message
  - with log files: tarball is created successfully
- pre-commit hooks passed during commit

---------

Signed-off-by: tenfyzhong <tenfy@tenfy.cn>
 (commit: cadf792)