CompatHelper: bump compat for MatrixMarket to 0.4 for package introduction-to-ldlfactorizations, (drop existing compat)

[github-actions]

This pull request changes the compat entry for the MatrixMarket package from 0.3 to 0.4 for package introduction-to-ldlfactorizations.
This drops the compat entries for earlier versions.

Note: I have not tested your package with this new compat entry.
It is your responsibility to make sure that your package tests pass before you merge this pull request.

[tmigot]

@geoffroyleconte

ERROR: Unsatisfiable requirements detected for package MatrixMarket [4d4711f2]:
 MatrixMarket [4d4711f2] log:
 ├─possible versions are: 0.3.0-0.4.0 or uninstalled
 ├─restricted to versions 0.4 by an explicit requirement, leaving only versions 0.4.0
 └─restricted by compatibility requirements with RipQP [1e40b3f8] to versions: 0.3.0-0.3.1 — no versions left
   └─RipQP [1e40b3f8] log:
     ├─possible versions are: 0.2.0-0.6.1 or uninstalled
     └─restricted to versions 0.6 by an explicit requirement, leaving only versions 0.6.0-0.6.1