ci: run semver-checks on a pull_request_target trigger

[aborgna-q]

Fixes the errors we've seen with dependabot PRs (and fork PRs) failing the checks.
See CQCL/hugrverse-actions#20

drive-by: Trigger the normal CI checks on any pull request, not only the ones targeting main

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 85.52%. Comparing base (c2c5752) to head (e81b6b8).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1661      +/-   ##
==========================================
- Coverage   85.52%   85.52%   -0.01%     
==========================================
  Files         136      136              
  Lines       25293    25293              
  Branches    22205    22205              
==========================================
- Hits        21633    21632       -1     
- Misses       2455     2456       +1     
  Partials     1205     1205              

Flag	Coverage Δ
python	92.42% <ø> (ø)
rust	84.56% <ø> (-0.01%)	⬇️

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