chore(*): add mathlib4 synchronization comments

[github-actions[bot]]

Regenerated from the port status wiki page. Relates to the following files:

• algebraic_topology.dold_kan.equivalence
• algebraic_topology.dold_kan.equivalence_pseudoabelian
• combinatorics.quiver.covering
• linear_algebra.quadratic_form.dual

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The following files have no module docstring, so I have not added a message in this PR

• control.basic
• control.monad.cont
• control.monad.writer
• control.traversable.derive
• data.array.lemmas
• data.bitvec.basic
• data.buffer.basic
• data.rbmap.basic
• data.rbmap.default
• data.rbtree.basic
• data.rbtree.default_lt
• data.rbtree.find
• data.rbtree.init
• data.rbtree.insert
• data.rbtree.main
• data.rbtree.min_max
• data.seq.computation
• data.seq.parallel
• data.seq.seq
• data.seq.wseq

Please make a PR to add a module docstring (for Lean3 and Lean4!), then I will add the freeze comment next time.

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The following files no longer exist in Lean 3' mathlib, so I have not added a message in this PR

• data.buffer.parser
• data.dlist
• data.vector
• init.algebra.classes
• init.algebra.functions
• init.algebra.order
• init.control.lawful
• init.data.int.bitwise
• init.data.int.comp_lemmas
• init.data.list.instances
• init.data.list.lemmas
• init.data.nat.bitwise
• init.data.nat.gcd
• init.data.nat.lemmas
• init.data.ordering.lemmas
• init.data.sigma.lex
• init.data.subtype.basic
• init.function
• init.ite_simp
• init.meta.well_founded_tactics
• oxford_invariants.«2021summer».week3_p1

In future we should find where they moved to, and check that the files are still in sync.

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I am a bot; please check that I have not put a comment in a bad place before running bors merge!