fix: sync uv.lock for v1.20.0 release

[martinge17]

Summary

The v1.20.0 release workflow is currently failing because release_versions.py expects version 1.20.0 of codex-lb but uv.lock contains version 1.20.0-beta.3. This PR just bumps that exact version so Docker images are build and uploaded to the registry.

Type of change

• fix: — bug fix (no behavior change beyond the bug)
• feat: — new user-facing feature or capability
• refactor: — internal refactor (no behavior change, no API change)
• docs: — documentation only
• chore: / ci: / build: — tooling, CI, packaging
• test: — test-only change
• Breaking change (also append ! after the type, e.g. feat!: or include BREAKING CHANGE: footer)

Linked issue: Fixes #1046

OpenSpec

• This PR includes / updates an OpenSpec change
• Not applicable — bug fix that matches the existing spec
• Not applicable — docs / CI / chore only
• This PR touches a codex-faithful path (image pipeline, request/response
  shape, SSE framing, OAuth flow) and preserves upstream-equivalent behavior

Change directory:

Changes

• Updates the editable codex-lb package version in uv.lock from 1.20.0-beta.3 to 1.20.0.

Test plan

python -m scripts.verify_release_version --tag "v1.20.0"

tag=v1.20.0
version=1.20.0
base_version=1.20.0
channel=stable
is_prerelease=false
pypi_version=1.20.0

Checklist

• Title is in Conventional Commits format (<type>(<scope>)?: <subject>).
• Linked the related issue / discussion above.
• Added or updated tests covering the change.
• Ran uv run pre-commit run local-ci --hook-stage manual --all-files or the relevant make <target> subset locally.
• If touching specs: openspec validate --specs passes and /opsx:verify is clean.
• CHANGELOG is not edited by hand (release-please handles it).