chore(deps): update ghcr.io/astral-sh/uv docker tag to v0.9.21 (#135)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

taskcluster/docker/python/Dockerfile

@@ -29,7 +29,7 @@ ENV SHELL=/bin/bash \
     PATH=/builds/worker/.local/bin:$PATH
 
 # uv
-COPY --from=ghcr.io/astral-sh/uv:0.9.18 /uv /bin/uv
+COPY --from=ghcr.io/astral-sh/uv:0.9.21 /uv /bin/uv
 # %ARG PYTHON_VERSIONS
 RUN uv python install $PYTHON_VERSIONS
 RUN chown -R worker:worker /builds/worker