Update quantecon-book-theme to test collapse styling fix

Co-authored-by: mmcky <8263752+mmcky@users.noreply.github.com>

Author: Copilot

environment.yml

@@ -7,7 +7,7 @@ dependencies:
   - pip
   - pip:
     - jupyter-book==1.0.3
-    - quantecon-book-theme==0.7.6
+    - git+https://github.com/QuantEcon/quantecon-book-theme@copilot/fix-299
     - sphinx-tojupyter==0.3.0
     - sphinxext-rediraffe==0.2.7
     - sphinx-reredirects==0.1.4