gh-38144: CI: Fix handling of deletions/renames; Build&Test: Uninstal…

…l/build changed packages; Linux Incremental: Update platforms

    
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Fixes handling of deletions/renames
- https://groups.google.com/g/sage-devel/c/tw6J8vU7IY0/m/IZxuGW8gBQAJ
- #36892 (comment)

When changes to packages are made, "CI Build&Test" now uses the same
logic as "CI Linux Incremental" for determining what SPKGs to uninstall
(so that spkg-configure.m4 is re-run) and what optional SPKGs to
install.

We update the platforms of "CI Linux Incremental" and remove the default
platform from there, to remove the duplication with "CI Build&Test".

- Also apparently fixes #37786

For a test run with a PR that actually makes changes to packages, see
- #38147

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### ⌛ Dependencies

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URL: #38144
Reported by: Matthias Köppe
Reviewer(s): Kwankyu Lee, Matthias Köppe