Upgrade Python 3.9 to 3.12

[hoch]

From the recent failure log:
https://github.com/WebAudio/web-audio-api/actions/runs/19301435663/job/57588563539

Successfully installed about-time-4.2.1 aiofiles-25.1.0 aiohappyeyeballs-2.6.1 aiohttp-3.13.2 aiosignal-1.4.0 alive-progress-3.3.0 async-timeout-5.0.1 attrs-25.4.0 bikeshed-6.1.1 cddlparser-0.5.0 certifi-2025.11.12 charset_normalizer-3.4.4 cssselect-1.3.0 frozenlist-1.8.0 graphemeu-0.7.2 html5lib-1.1 idna-3.11 isodate-0.7.2 kdl-py-1.2.0 lxml-6.0.2 multidict-6.7.0 pillow-11.3.0 propcache-0.4.1 pygments-2.19.2 requests-2.32.5 result-0.17.0 setuptools-80.9.0 six-1.17.0 tenacity-9.1.2 typing-extensions-4.15.0 urllib3-2.6.1 webencodings-0.5.1 widlparser-1.4.0 yarl-1.22.0
Bikeshed now requires Python 3.12 or higher; you are on 3.9.25.
    For instructions on how to set up a pyenv with 3.12, see:
    https://speced.github.io/bikeshed/#installing

Upgrading 3.12 might cause some unexpected changes, so we need to monitor the build carefully.

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Preview | Diff

[hoch]

The Bikeshed's support of SpecRef and "microphone" is flawed at the moment, so let's just land this with a plain text of "microphone". We have other (pre-exisiting) instances of "microphone" as well, so this is not a regression.

Also the newest version of Bikeshed on Python 3.12 changed the build error log format, so we have to reproduce the expected-errs.txt file again.

[padenot]

Thanks!