test: update osname for edge deployments

[mcattamoredhat]

This pull request includes:

In order to align with PR distro/rhel: unify osname for edge deployments, it is suggested to update edge-installer, edge-simplified-installer, and edge-raw-image tests with the corresponding osname value.

• adequate testing for the new functionality or fixed issue
• adequate documentation informing people about the change such as
  • submit a PR for the READMEs listed here
  • submit a PR for the osbuild.org website repository if this PR changed any behavior not covered by the automatically updated READMEs

[achilleas-k]

Thanks for updating this. I made a note to do it myself when importing the changes here but it must have gotten lost in all the work from the last few weeks. Sorry about that.