CI: Update distros

[evelikov]

Going through the distributions list:

• remove: Alpine 3.14 and earlier (3.14 is EOL next month)
• add: Apline 3.15 - 3.17
• keep: CentOS 7 is EOL no newer version officially has docker images (could be wrong here)
• keep: Ubuntu 18.04 (EOL this month) - should we drop this @xnox @anbe42
• keep: Debian 9 (EOL 2020, LTS 2022) - planning to keep until Debian 12 is released in a few months

@xuzhen @scaronni should we add some Suse/Fedora/other versions in the mix?

[evelikov]

Looking at the failures, a few interesting bits became apparent:

• the good: tests have a hard-coded distro/module compression list - some distros are not tested in CI (fedora/rhel/ovm/suse/sles/opensuse)
• the good: Alpine has switched to .gz compressed modules \o/
• the bad: vast majority of distros do not compress the kernel modules
• the ugly: module compression detection is broken - relies on the potentially missing modules.dep (instead of the CONFIG)
• the ugly: we mostly get away with ^^ since we always check for both compressed and uncompressed modules

[evelikov]

Let's go with a quick fix for now by adding the .gz expectation for Alpine.

I'm moderately contemplating about ripping out some/all of the custom installation (which includes the module stripping/signing) in favour of make module_install. On a quick testing it just works and does the right thing.

@scaronni do you recall why module_install isn't used in the first place? Do you have any particularly complex/convoluted module that confuses dkms?