test: Enable OSTree simplified installer test on RHEL 9

[henrywang]

coreos-installer-0.10.1-2.el9.x86_64.rpm is available on RHEL 9 nightly, it's time to enable OSTree simplified installer test

[henrywang]

@achilleas-k Oh, my. I got Failed to get compose type "edge-simplified-installer": invalid image type: edge-simplified-installer error. Looks edge-simplified-installer should be enabled on RHEL 9.

osbuild-composer/internal/distro/rhel90/distro.go

Line 621 in d3a3dba

// edgeSimplifiedInstallerImgType := imageType{

[achilleas-k]

@achilleas-k Oh, my. I got Failed to get compose type "edge-simplified-installer": invalid image type: edge-simplified-installer error. Looks edge-simplified-installer should be enabled on RHEL 9.

osbuild-composer/internal/distro/rhel90/distro.go

Line 621 in d3a3dba

// edgeSimplifiedInstallerImgType := imageType{

I disabled the simplified installer type because the coreos-installer package wasn't available yet in RHEL 9. It became available right before we merged the PR. @diaasami's PR #1744 was meant to enable the image type and test but that's based on the previous distro definition which is now RHEL 9 beta. There's probably not much sense in reusing that PR. We can just revert commit a8eb58b.

[henrywang]

Close this PR due to duplicated with PR #2015. Thanks @achilleas-k!