Fix CI

[pazeshun]

Currently, Compile MuxTo github action fails (e.g., https://github.com/arduino/ArduinoCore-megaavr/actions/runs/11121101633), so we cannot follow #103 (comment).
This PR tries to fix that situation.

• upload-artifact@v2 and download-artifact@v2 failed because they are deprecated, so this PR upgrades them to the latest version (v4). The deprecation notice is here: https://github.blog/changelog/2024-02-13-deprecation-notice-v1-and-v2-of-the-artifact-actions/
  • upload-artifact@v4 requires artifact names to be unique, so this PR fixes them
    (cf. Conflict: an artifact with this name already exists on the workflow run simonw/shot-scraper#141)
• Installing MattairTech_Arduino:samd failed because the link to its json (https://www.mattairtech.com/software/arduino/package_MattairTech_index.json) is broken. We have its archive (https://web.archive.org/web/20210308115824/https://www.mattairtech.com/software/arduino/package_MattairTech_index.json), but some of the indicated URLs (e.g., https://www.mattairtech.com/software/arduino/MattairTech_samd_1.6.5-mt1.zip) are not archived:
  http://web.archive.org/web/*/https://www.mattairtech.com/software/arduino/*
  so we cannot install MattairTech_Arduino:samd via the archived json.
  This PR avoids that problem by installing Fab_SAM_Arduino:samd, the successor of MattairTech_Arduino:samd. This workaround requires some patches to ArduinoCore-samd, so I'm not sure this is a good way.

[pazeshun]

I'm not sure why, but Compile MuxTO action does not run on this PR.
See https://github.com/pazeshun/ArduinoCore-megaavr/actions/workflows/compile-muxto.yml?query=branch%3Afix-ci for its result.

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