Rename AlmaLinux.gns3a to almalinux.gns3a

[b-ehlers]

As (almost) all appliances are all lowercase, this PR renames AlmaLinux.gns3a to almalinux.gns3a.

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Before submitting a pull request, please check the following.

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When updating an existing appliance:

• [x] The new version is on top.
• [x] The filenames in the "images" section are unique, to avoid appliances / version overwriting each other.
• [x] If you forked the repo, running check.py doesn't drop any errors for the updated file.