Advance RFC #1009 `"Move the deprecation workflow library to be installed in apps by default"` to Stage Ready for Release #1247

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Stage must be 'Exploring' (via label) for new RFC before merging	0s
Only one RFC can be added in a PR	0s
RFC must be in only one stage before merging (labels)	0s
Verify Accepted PR URL is correct	0s
Filename matches RFC number	0s
Frontmatter stage must be 'accepted' before merging	0s
	8s

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