chore(*): add mathlib4 synchronization comments (#17806)
Regenerated from the [port status wiki page](https://github.com/leanprover-community/mathlib/wiki/mathlib4-port-status).
Relates to the following PRs:
* `algebra.divisibility.basic`: https://github.com/leanprover-community/mathlib4/pull/833
* `algebra.group.with_one.defs`: https://github.com/leanprover-community/mathlib4/pull/841
* `algebra.hom.commute`: https://github.com/leanprover-community/mathlib4/pull/831
* `algebra.hom.group`: https://github.com/leanprover-community/mathlib4/pull/659
* `algebra.hom.units`: https://github.com/leanprover-community/mathlib4/pull/745
* `algebra.ring.basic`: https://github.com/leanprover-community/mathlib4/pull/830
* `category_theory.natural_isomorphism`: https://github.com/leanprover-community/mathlib4/pull/820
* `combinatorics.quiver.connected_component`: https://github.com/leanprover-community/mathlib4/pull/836
* `combinatorics.quiver.subquiver`: https://github.com/leanprover-community/mathlib4/pull/828
Co-authored-by: Johan Commelin <johan@commelin.net>
