bugfix(pitr): fix test case show no record

[Xu-Wentao]

Type of change:

• Bugfix
• New feature provided
• Improve performance
• Backport patches

What this PR does / why we need it:

fix a test case bug, set 2 variables CSN and RecordID to "" to make sure the test to run as expected.

Pre-submission checklist:

• Did you explain what problem does this PR solve? Or what new features have been added?
• Have you added corresponding test cases?
• Have you modified the corresponding document?

[codecov-commenter]

Codecov Report

Merging #297 (fbdd2ad) into main (46be6a7) will decrease coverage by 13.31%.
The diff coverage is 49.06%.

@@             Coverage Diff             @@
##             main     #297       +/-   ##
===========================================
- Coverage   62.36%   49.06%   -13.31%     
===========================================
  Files           2        8        +6     
  Lines         279      856      +577     
===========================================
+ Hits          174      420      +246     
- Misses        103      368      +265     
- Partials        2       68       +66     

Impacted Files	Coverage Δ
pitr/cli/internal/pkg/shardingsphere-proxy.go	0.00% <0.00%> (ø)
pitr/cli/internal/pkg/local-storage.go	42.73% <42.73%> (ø)
pitr/cli/internal/cmd/restore.go	44.58% <44.58%> (ø)
pitr/cli/internal/cmd/show.go	56.09% <56.09%> (ø)
pitr/cli/internal/cmd/backup.go	58.87% <58.87%> (ø)
pitr/cli/internal/pkg/agent-server.go	72.54% <72.54%> (ø)
pitr/cli/pkg/gsutil/conn.go	76.47% <76.47%> (ø)
pitr/cli/pkg/stringutil/rand_string.go	91.30% <91.30%> (ø)

... and 1 file with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[mlycore]

LGTM