Install python versions on github action for tests (#4844)

## Changes
- Add "make install-pythons" to install Python versions used by tests
via uv.
- Enable it on CI to make tests pass.

Perf impact is negligible:
> Installed 5 versions in 2.57s

## Why

In #4830 we've set UV_OFFLINE=true
which disables Python downloading.

## Tests
CI checks on this PR.

Author: denik

.github/actions/setup-build-environment/action.yml

@@ -34,6 +34,10 @@ runs:
       with:
         version: "0.8.9"
 
+    - name: Install Python versions for tests
+      run: make install-pythons
+      shell: bash
+
     - name: Install ruff (Python linter and formatter)
       uses: astral-sh/ruff-action@4919ec5cf1f49eff0871dbcea0da843445b837e6 # v3.6.1
       with:

Makefile

@@ -70,6 +70,10 @@ links:
 checks: tidy ws links
 
 
+.PHONY: install-pythons
+install-pythons:
+	uv python install 3.9 3.10 3.11 3.12 3.13
+
 # Run short unit and acceptance tests (testing.Short() is true).
 .PHONY: test
 test: test-unit test-acc