Restore uv pip install in scala and python CI jobs

[Yicong-Huang]

What happened?

The Build workflow's scala and python jobs lost the uv pip install --system switch that #4521 introduced. Both jobs now use the slower stock pip install again, regressing CI install speed for every PR.

The change was reverted in #4597 ("ci: merge binary license checks into build workflow"); during the inline of the binary-license-check steps the python -m pip install uv and uv pip install --system -r ... lines from #4521 were rewritten back to python -m pip install --upgrade pip and pip install -r .... Each subsequent rebase has carried the older lines forward.

How to reproduce?

1. Open .github/workflows/build.yml on main (commit 8e40078e2f at time of writing).
2. Look at the scala job's "Install dependencies" step (~line 162) and the python job's "Install dependencies" step (~line 261).
3. Both run python -m pip install --upgrade pip followed by pip install -r ....
4. Compare with perf(ci): use uv pip for faster Python dep install #4521 — those steps used to be python -m pip install uv followed by uv pip install --system -r ....

Version

1.1.0-incubating (Pre-release/Master)

Commit Hash (Optional)

8e40078

Relevant log output

# Current build.yml scala job (regressed)
- name: Install dependencies
  run: |
    python -m pip install --upgrade pip
    if [ -f amber/requirements.txt ]; then pip install -r amber/requirements.txt; fi
    if [ -f amber/operator-requirements.txt ]; then pip install -r amber/operator-requirements.txt; fi

# Should be (per #4521)
- name: Install dependencies
  run: |
    python -m pip install uv
    if [ -f amber/requirements.txt ]; then uv pip install --system -r amber/requirements.txt; fi
    if [ -f amber/operator-requirements.txt ]; then uv pip install --system -r amber/operator-requirements.txt; fi