gh-36999: Rename `install-requires.txt` to `version_requirements.txt`
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As discussed in #36982:
- the name "install-requires" has become outdated with the transition
to the new names set by the `pyproject.toml` format (see https://setupto
ols.pypa.io/en/latest/userguide/dependency_management.html#declaring-
required-dependency, compare the tabs "pyproject.toml" vs. "setup.cfg")
- this will help with https://github.com/sagemath/sage/issues/35890, as
GitHub will be able to just read the `version_requirements.txt` files
https://github.com/sagemath/sage/pull/36982#issuecomment-1874857075
Notes for reviewers:
- **This is a simple, limited-scope improvement and not intended as a
long-term commitment to the format of the files in build/pkgs/....**
- PRs #37430, #37350, #36740 remove direct access to build/pkgs in favor
of using the sage_bootstrap API (sage --package).
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### :hourglass: Dependencies
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- Depends on https://github.com/sagemath/sage/pull/37401
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URL: https://github.com/sagemath/sage/pull/36999
Reported by: Matthias Köppe
Reviewer(s): Dima Pasechnik, Kwankyu Lee, Nathan Dunfield
