ci: run pr checks only on prs #9

Job	Run time
linux (stable, d)	53s
macos (stable)	38s
linux (stable, d,images)	1m 14s
macos (beta)	24s
windows (stable)	2m 27s
linux (stable, z)	59s
macos (stable minus 6 releases)	48s
linux (stable, z,images)	1m 24s
windows (beta)	2m 4s
linux (stable, z,d)	1m 14s
windows (stable minus 6 releases)	1m 33s
linux (beta, d)	1m 23s
linux (beta, d,images)	56s
linux (beta, z)	37s
linux (beta, z,images)	1m 3s
linux (beta, z,d)	45s
linux (stable minus 2 releases, d)	32s
linux (stable minus 2 releases, d,images)	1m 0s
linux (stable minus 2 releases, z)	58s
linux (stable minus 2 releases, z,images)	1m 29s
linux (stable minus 2 releases, z,d)	1m 2s
	23m 23s

Provide feedback