Add Copilot instructions for release PRs #888

Job	Run time
Rust analysis (ubuntu-latest, default)	1m 36s
Rust analysis (ubuntu-latest, stable-v2.19.3)	1m 27s
Rust analysis (ubuntu-latest, linked)	1m 43s
Rust analysis (ubuntu-latest, stable-v2.22.1)	1m 54s
Rust analysis (ubuntu-latest, nightly-latest)	1m 48s
	8m 28s

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