Simplify return codes to return 1 if any vulnerability related error

[another-rex]

Fixes #676

• Return 0 if there are no findings or errors.
• Return 1 if there are any findings (license or vulns).
• Return 128 if no packages are found.

[codecov-commenter]

Codecov Report

Attention: 1 lines in your changes are missing coverage. Please review.

Comparison is base (8c5634d) 78.50% compared to head (621291b) 78.74%.

Files	Patch %	Lines
cmd/osv-reporter/main.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #677      +/-   ##
==========================================
+ Coverage   78.50%   78.74%   +0.24%     
==========================================
  Files          82       82              
  Lines        5890     5853      -37     
==========================================
- Hits         4624     4609      -15     
+ Misses       1068     1046      -22     
  Partials      198      198              

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[josieang]

Thanks for doing this!

[oliverchang]

thanks Rex!