[SW-562] update sphinx workflow

[jcao-bdai]

This PR intends to fix the sphinx workflow error observed on main branch, e.g. https://github.com/bdaiinstitute/spatialmath-python/actions/runs/6882816142

Changes have been tested using a test commit where the if ... != pull_request condition was removed and several "push" steps commented out to trigger the spinx step without impacting downstream:

• test commit: https://github.com/bdaiinstitute/spatialmath-python/pull/97/commits/e3853d405014be621f4b575cdbf2ea8266138d24
• the triggered and passed workflow https://github.com/bdaiinstitute/spatialmath-python/actions/runs/6922110660

Details are documented in https://theaiinstitute.atlassian.net/browse/SW-562

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (e2d44b1) 75.62% compared to head (56ce2b4) 75.62%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #97 +/- ## ======================================= Coverage 75.62% 75.62% ======================================= Files 24 24 Lines 5132 5132 ======================================= Hits 3881 3881 Misses 1251 1251 ```

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