Revert "pin pandas in CI"

This reverts commit ef7b354.

.github/workflows/collab.yml

@@ -28,7 +28,7 @@ jobs:
       - name: Install Build Software
         shell: bash -l {0}
         run: |
-          pip install pandas==2.1.4 jupyter-book==0.15.1 docutils==0.17.1 quantecon-book-theme==0.7.1 sphinx-tojupyter==0.3.0 sphinxext-rediraffe==0.2.7 sphinx-exercise==0.4.1 sphinxcontrib-youtube==1.1.0 sphinx-togglebutton==0.3.1 arviz==0.13.0 sphinx_proof==0.1.3
+          pip install jupyter-book==0.15.1 docutils==0.17.1 quantecon-book-theme==0.7.1 sphinx-tojupyter==0.3.0 sphinxext-rediraffe==0.2.7 sphinx-exercise==0.4.1 sphinxcontrib-youtube==1.1.0 sphinx-togglebutton==0.3.1 arviz==0.13.0 sphinx_proof==0.1.3
       # Build of HTML (Execution Testing)
       - name: Build HTML
         shell: bash -l {0}