download cosign releases from GitHub rather than GCS #289

Job	Run time
Install Cosign v0.6.0 and test presence in path with pre installed libpcsclite1 package (ubuntu-l...	14s
Install Cosign and test presence in path (macos-latest)	12s
Install Cosign and test presence in path (ubuntu-latest)	4s
Install Cosign and test presence in path (windows-latest)	18s
Install Custom Cosign and test presence in path (macos-latest)	5s
Install Custom Cosign and test presence in path (ubuntu-latest)	6s
Install Custom Cosign and test presence in path (windows-latest)	1s
Install Cosign v0.6.0 and test presence in path (macos-latest)	6s
Install Cosign v0.6.0 and test presence in path (ubuntu-latest)	5s
Install Cosign v0.6.0 and test presence in path (windows-latest)	11s
Install Custom Cosign and test presence in path (macos-latest)	30s
Install Custom Cosign and test presence in path (ubuntu-latest)	5s
Install Custom Cosign and test presence in path (windows-latest)	17s
Install Custom Cosign and test presence in path with custom root dir (ubuntu-latest)	6s
Try to install a wrong Cosign (macos-latest)	11s
Try to install a wrong Cosign (ubuntu-latest)	6s
Try to install a wrong Cosign (windows-latest)	12s
Try to install cosign with go 1.19	3m 21s
Try to install cosign with go 1.20	4m 11s
Try to install cosign with go 1.19	3m 1s
Try to install cosign with go 1.20	2m 59s
Try to install cosign with go 1.19	10m 57s
Try to install cosign with go 1.20	7m 1s
Install existing release of Cosign and test presence in path (ubuntu-latest)	6s
	34m 25s

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