Add with to PlainYearMonth #752

Job	Run time
Documentation	37s
Test FFI (stable, ubuntu-latest)	1m 1s
Test feature matrix	2m 3s
Test (stable, ubuntu-latest)	1m 10s
Lint	19s
Test (stable, macos-latest)	25s
MSRV	28s
Test (stable, windows-latest)	1m 49s
	7m 52s

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