dataframely: install pandas for the benches test collection

tests/benches/conftest.py imports pandas at module load, which pytest
collection needs even though the benchmark suite itself is not gated
by -m "not with_optionals". pypi.riseproject.dev already publishes a
cp310 riscv64 wheel for pandas (up through 2.3.2, before 3.0's
requires-python bump to >=3.11), so this resolves to a prebuilt wheel
rather than a from-source build.

Author: luhenry

.github/workflows/build-dataframely.yml

@@ -109,7 +109,7 @@ jobs:
         run: |
           uv pip install --force-reinstall dist/*.whl
           uv pip install --extra-index-url https://pypi.riseproject.dev/simple/ \
-            pytest pytest-benchmark pytest-mock numpy
+            pytest pytest-benchmark pytest-mock numpy pandas
 
           # cd out of the checkout first (gotcha 25/218): dataframely's pure-Python
           # wrapper package lives directly at the checkout root ($GITHUB_WORKSPACE),