fix: upgrade pip before installing uv in alpine build

[thomasrockhu-codecov]

Summary

• The Build and Publish CLI Release Alpine matrix legs failed at Run in Docker (e.g. run 28973879139) with ERROR: No matching distribution found for uv.
• Root cause: alpine:3.14 ships system pip 20.3.4, which predates musllinux wheel-tag support (PEP 656, added in pip 21.3). Since uv only ships musl builds as musllinux wheels, pip install uv --only-binary uv finds no compatible candidate and fails.
• Fix: upgrade pip first so it recognizes musllinux tags and can install the uv wheel. Alpine 3.14 has no PEP 668 EXTERNALLY-MANAGED marker (that arrived in Alpine 3.19 / Python 3.11), so no --break-system-packages is required. --only-binary uv is kept so pip never falls back to a source build.

Test plan

• Re-run the release (or the build_assets workflow with release: true) and confirm the Alpine x86_64 and arm64 legs build and upload assets successfully.

[codecov]

❌ 1 Tests Failed:

Tests completed	Failed	Passed	Skipped
723	1	722	1

View the full list of 1 ❄️ flaky test(s)

api.temp.calculator.test_calculator::test_divide

Flake rate in main: 100.00% (Passed 0 times, Failed 1265 times)

Stack Traces | 0.001s run time

def
                test_divide():
                > assert Calculator.divide(1, 2) == 0.5
                E assert 1.0 == 0.5
                E + where 1.0 = <function Calculator.divide at 0x104c9eb90>(1, 2)
                E + where <function Calculator.divide at 0x104c9eb90> = Calculator.divide
                .../temp/calculator/test_calculator.py:30: AssertionError

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