Bump macos runner from 11 to 12

[tinaboyce]

Closes #1302

[codecov-commenter]

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Codecov Report

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

Project coverage is 42.19%. Comparing base (99d6fe4) to head (a2d7f3c). Report is 24 commits behind head on master.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #1304 +/- ## ======================================= Coverage 42.19% 42.19% ======================================= Files 54 54 Lines 6456 6456 ======================================= Hits 2724 2724 Misses 3283 3283 Partials 449 449 ``` | [Flag](https://app.codecov.io/gh/Versent/saml2aws/pull/1304/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Versent) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/Versent/saml2aws/pull/1304/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Versent) | `42.19% <ø> (ø)` | | 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=Versent#carryforward-flags-in-the-pull-request-comment) to find out more.

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[tinaboyce]

Oops, my bad, I didn't see the discussion until now.