go/runtime/bundle: Don't abort when some manifests cannot be loaded

[kostko]

When upgrading from earlier versions the exploded bundle directory may contain non-bundle subdirectories which should not cause the loader to fail.

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[codecov]

Codecov Report

Attention: Patch coverage is 0% with 10 lines in your changes missing coverage. Please review.

Project coverage is 64.69%. Comparing base (b7bd71a) to head (7a3d8fc).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
go/runtime/bundle/manager.go	0.00%	10 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #6044      +/-   ##
==========================================
- Coverage   65.26%   64.69%   -0.58%     
==========================================
  Files         635      635              
  Lines       64604    64624      +20     
==========================================
- Hits        42167    41809     -358     
- Misses      17525    17907     +382     
+ Partials     4912     4908       -4     

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[peternose]

This solves the problem, but the folder structure will remain invalid indefinitely. If any abnormalities occur, the cached folder should be completely wiped. Maybe we do that in another task.

[kostko]

Removing unknown stuff without letting the user know is always somewhat dangerous as the data could be useful. Maybe it is ok in this case since the whole directory is a cache, but let's defer this to another PR.