Exclude uv/pip installer versions from generated constraints files

[bramhanandlingala]

closes: #70231

What

uv and pip versions were being written into generated constraints
files via pip freeze, even though they're build tools, not Airflow
dependencies.

Fix

Added "uv==" and "pip==" to the exclusion list in
freeze_distributions_to_file() (scripts/in_container/run_generate_constraints.py),
matching the same exclusion already used in uninstall_all_packages()
in the same file.

Why this fixes the issue

Constraints files and published Docker images are refreshed on
different, independent cadences — a rebuild of one doesn't
necessarily happen alongside the other. Capturing uv's version in
constraints caused it to drift from whatever version actually shipped
in the image, exactly as reported in #70231. Excluding it removes
that class of mismatch at the source.

[raphaelauv]

Hey , thanks for the fix

but about published Docker images are built once and never rebuilt , this is not true, it happened several times

example : docker image of 3.3.0 was re-built and re-publish

[bramhanandlingala]

@raphaelauv

Good catch, thanks — updated the description. Removed the "never rebuilt" claim and reworded it to focus on the actual point: constraints and image rebuilds happen on independent cadences, so there's no guarantee uv's captured version matches what ships in a given image.