text: Title: Update sphinx and the related packages
  Body: **Description of the issue**
  
  **Problem:** The current requirements pin sphinx to version `3.2.*` which is too old for recent releases of its alabaster theme package - see the CI error [here](https://github.com/quantumlib/Cirq/actions/runs/7452039565/job/20274451752?pr=6399#step:5:15)
  
  **Solution:** Update sphinx and any dependent packages to their recent versions.  Sphinx is currently at version 7.2.6, https://pypi.org/project/Sphinx/#history.
  
  **Cirq version**
  
  1.4.0.dev at d33b1a71ac9721e762a2fa1b9e9871edfe187a3c.
  