gh-35460: Update developer guide for workflows on github
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### :books: Description
Our developer guide needs to be updated incorporating the new workflows
on GitHub. Here is the updated developer guide.
I know this needs more editing, but at least it reached the point where
other eyes would catch more errors, typos, and defects than mine alone.
So please examine the built documentation and report errors, typos, and
defects. If you think a major addition such as a new section is needed,
then please open a new PR that builds on this PR and provide your own
writing.
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- [ ] I have updated the documentation accordingly.
### :hourglass: Dependencies
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URL: https://github.com/sagemath/sage/pull/35460
Reported by: Kwankyu Lee
Reviewer(s): Kwankyu Lee, Matthias Köppe, Sebastian Oehms, Tobias Diez
Committer
Release Manager
