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 https://github.com/CQCL/hugrverse-actions/issues/20

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

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

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

Additional details and impacted files

```diff @@ 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](https://app.codecov.io/gh/CQCL/hugr/pull/1661/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CQCL) | Coverage Δ | | |---|---|---| | [python](https://app.codecov.io/gh/CQCL/hugr/pull/1661/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CQCL) | `92.42% <ø> (ø)` | | | [rust](https://app.codecov.io/gh/CQCL/hugr/pull/1661/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CQCL) | `84.56% <ø> (-0.01%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=CQCL#carryforward-flags-in-the-pull-request-comment) to find out more.

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