Pin Tutor to known-good commit for master CI matrix entry

[Copilot]

CI for the master matrix entry was tracking Tutor main live, which picked up a packaging toolchain regression (introduced in overhangio/tutor@f9c2a39) that causes mysqlclient==2.2.8 to fail building with ValueError: invalid pyproject.toml config: project.license.

Change

Pin Tutor to commit 859b5bc394565de25abbee7e83f4d1dc5ae2f505 (known-good, pre-regression) instead of cloning --branch=main:

- git clone --branch=main https://github.com/overhangio/tutor.git
- pip install -e "./tutor"
+ # Pin to a known-good commit until the upstream packaging regression is fixed.
+ git clone https://github.com/overhangio/tutor.git
+ cd tutor
+ git checkout 67b79820e54a4b29e39e0c93cf4a484c322afe55
+ cd ..
+ pip install -e "./tutor"

This restores reproducibility for the master job without changing behavior for the teak or ulmo matrix entries. The pin should be relaxed once the upstream regression is resolved in Tutor.

[Copilot]

Pull request overview

Pins the Tutor version used by the GitHub Actions CI matrix for the master Open edX branch to a specific commit, avoiding breakages from tracking Tutor’s moving main branch and restoring reproducible CI runs.

Changes:

• Replace git clone --branch=main with a plain clone plus an explicit git checkout <commit> for the master matrix entry.
• Add an inline comment documenting the reason for the pin (upstream packaging regression).

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