ci: replace Cirrus CI with GitHub Actions #16

Job	Run time
path-filter	5s
Common: Test	10m 11s
Image: Skopeo openpgp	10m 30s
Image: Test default	3m 58s
Image: Test openpgp	3m 57s
Image: Cross	1m 22s
Storage: gofix	59s
Storage: fedora-current overlay-transient	13m 3s
Storage: fedora-current vfs	13m 7s
Image: Test sequoia	3m 54s
Image: Skopeo sequoia	10m 56s
Storage: fedora-current overlay	14m 18s
Image: Skopeo default	11m 26s
Storage: fedora-current fuse-overlay	12m 58s
Storage: Cross	4m 51s
Storage: fedora-current fuse-overlay-whiteout	13m 24s
Storage: debian-sid fuse-overlay	12m 35s
Storage: fedora-current btrfs	13m 0s
Storage: debian-sid btrfs	12m 59s
Storage: debian-sid vfs	12m 47s
Storage: debian-sid overlay	12m 36s
Storage: debian-sid fuse-overlay-whiteout	13m 43s
Total Success	2s
	3h 26m 41s

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