fix: invalid behavior on sid/alternative in 5.3.4/99.5.4.5.1

[sinrazon]

On Debian Sid / alternative distributions (such as Ubuntu), these checks would fail with sid: integer expression expected, which is to be expected since $DEB_MAJ_VER is set to a string, not an integer.

This small PR fixes that in a similar fashion to other checks in the source tree.

[ThibaultDewailly]

Hello and welcome to this repository !

Please code the tests associated to the Pull request, in order to validate the behavior you are introducing

[ThibaultDewailly]

Blocker : Associated tests are mandatory

[sinrazon]

As requested, I've reworked this PR to include related tests.

A few notes about these changes :

• @ThibaultDewailly suggested inverting the $DEB_MAJ_VER condition, to check for Debian 11 first, then sid; however, doing so does not fix the aforementioned error (string being tested against an integer), so this change was not made.
• There is no test utility to "mock" a Debian version, and the $DEB_MAJ_VER utility is outside of the individual test scope, which is not overridable. The accepted solution is to monkey-patch /etc/debian_version on the fly.
• A lot of tests were missing for both of these checks, so I've added them based on similar checks + new tests for Debian Sid.
• A couple of tweaks were needed to make the apply() function work for these scripts. I think the lack of sufficient testing broke them a while ago.

All these changes were tested against Debian 10/11/12.

Please let me know if anything more is needed.