Update Android CI macOS version to 12

[seladb]

Android builds that use macos-11 stopped working. Apparently this version is being deprecated:
https://docs.github.com/en/actions/using-github-hosted-runners/about-github-hosted-runners/about-github-hosted-runners#standard-github-hosted-runners-for-public-repositories

The macos-11 label has been deprecated and will no longer be available after 28 June 2024.

We only use it in Android builds.

I tried upgrading to macOS 13 but it failed: https://github.com/seladb/PcapPlusPlus/actions/runs/9642620294/job/26590863567

When I'll have more time I'll try to fix it, but for now let's upgrade to macOS 12?

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.63%. Comparing base (a31348b) to head (e182886).

Additional details and impacted files

@@           Coverage Diff           @@
##              dev    #1467   +/-   ##
=======================================
  Coverage   82.63%   82.63%           
=======================================
  Files         171      171           
  Lines       22614    22614           
  Branches     8559     8559           
=======================================
  Hits        18686    18686           
- Misses       3097     3112   +15     
+ Partials      831      816   -15     

Flag	Coverage Δ
alpine317	72.73% <ø> (+<0.01%)	⬆️
fedora37	72.73% <ø> (+0.04%)	⬆️
macos-12	61.49% <ø> (ø)
macos-13	60.56% <ø> (ø)
macos-14	60.56% <ø> (ø)
mingw32	70.69% <ø> (ø)
mingw64	70.69% <ø> (ø)
npcap	83.91% <ø> (ø)
rhel93	72.74% <ø> (+0.04%)	⬆️
ubuntu1804	75.25% <ø> (+<0.01%)	⬆️
ubuntu2004	73.65% <ø> (-0.05%)	⬇️
ubuntu2004-zstd	73.65% <ø> (ø)
ubuntu2204	72.55% <ø> (ø)
ubuntu2204-icpx	59.03% <ø> (ø)
unittest	82.63% <ø> (ø)
windows-2019	83.93% <ø> (ø)
windows-2022	83.93% <ø> (ø)
winpcap	83.89% <ø> (-0.02%)	⬇️
xdp	60.18% <ø> (ø)

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