Only run CI on latest commit of PR branches (#714) #1272

Job	Run time
set-msrv / set-msrv	3s
minimal-versions / minimal-versions	42s
build (1.85.0, wasm32-unknown-unknown)	22s
build (stable, thumbv7em-none-eabi)	24s
build (stable, wasm32-unknown-unknown)	16s
build (1.85.0, thumbv7em-none-eabi)	21s
test (stable)	32s
test (1.85.0)	30s
	3m 10s

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