[Merged by Bors] - chore(Algebra/GroupWithZero/Opposite): Move instances from Algebra.Ring.Opposite

[YaelDillies]

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[github-actions]

PR summary d4ae7c661e

Import changes for modified files

Dependency changes

File	Base Count	Head Count	Change
Mathlib.Algebra.SMulWithZero	318	316	-2 (-0.63%)

Import changes for all files

Files	Import difference
Too many changes (2617)!

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Declarations diff

No declarations were harmed in the making of this PR! 🐙

You can run this locally as follows

## summary with just the declaration names:
./scripts/declarations_diff.sh <optional_commit>

## more verbose report:
./scripts/declarations_diff.sh long <optional_commit>

[mattrobball]

Please shake and merge. Thanks.

bors delegate+

[mathlib-bors]

✌️ YaelDillies can now approve this pull request. To approve and merge a pull request, simply reply with bors r+. More detailed instructions are available here.

[YaelDillies]

Thanks for the quick turnaround!

bors merge

[mathlib-bors]

Pull request successfully merged into master.

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