Improve handling of mirror renw

[dveeden]

What problem does this PR solve?

GetComponentManifest() can return a nil manifest if it returns an error. newMirrorRenewCmd() ignores expiration errors when calling GetComponentManifest(). It should make sure that the manifest is not nil when calling RenewManifest().

ref #2398

What is changed and how it works?

Check List

Tests

• Manual test (add detailed scripts or steps below)

Release notes:

Bugfix: The `tiup mirror renew` command could segfault on expired manifests.

[ti-chi-bot]

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[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 3 lines in your changes are missing coverage. Please review.

Project coverage is 55.93%. Comparing base (6f01692) to head (d11e769).

❗ Current head d11e769 differs from pull request most recent head 5ab50e4. Consider uploading reports for the commit 5ab50e4 to get more accurate results

Files	Patch %	Lines
cmd/mirror.go	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2400      +/-   ##
==========================================
- Coverage   55.95%   55.93%   -0.02%     
==========================================
  Files         329      329              
  Lines       35221    35224       +3     
==========================================
- Hits        19706    19702       -4     
- Misses      13143    13149       +6     
- Partials     2372     2373       +1     

Flag	Coverage Δ
tiup	33.58% <0.00%> (-0.06%)	⬇️
unittest	22.15% <0.00%> (-0.01%)	⬇️

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[kaaaaaaang]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-04-09 12:20:06.272743816 +0000 UTC m=+964867.800284360: ☑️ agreed by kaaaaaaang.