Add APT multiarch preflight regression test

[TobiPeterG]

What does this PR do?

Adds regression coverage for pkg.installed handling of an already
installed native-architecture APT package whose explicit package name
contains an architecture suffix.

The test reproduces the NVIDIA container package scenario with:

• libnvidia-container-tools
• libnvidia-container1:amd64

APT reports the latter from pkg.list_pkgs() as the normalized
libnvidia-container1 name. The test verifies that pkg.installed
recognizes both packages as already installed and does not call
pkg.install.

The test passes on the current 3006.x branch and fails on v3006.26,
where libnvidia-container1:amd64 is incorrectly passed to
pkg.install as an installation target.

What issues does this PR fix or reference?

References #68932 and #69604.
Closes #70209

Previous Behavior

The v3006.26 preflight incorrectly considered an installed native
multiarch package missing when the desired name contained :amd64 but
pkg.list_pkgs() returned its normalized name.

New Behavior

The existing normalized-name fallback is covered by a regression test
using the original two-package reproduction.

Merge requirements satisfied?

• Docs — not applicable; test-only change
• Changelog — not applicable; test-only change
• Tests written/updated

Commits signed with GPG?

No

[welcome]

Hi there! Welcome to the Salt Community! Thank you for making your first contribution. We have a lengthy process for issues and PRs. Someone from the Core Team will follow up as soon as possible. In the meantime, here's some information that may help as you continue your Salt journey.
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[TobiPeterG]

Hi there! Welcome to the Salt Community! Thank you for making your first contribution. We have a lengthy process for issues and PRs. Someone from the Core Team will follow up as soon as possible. In the meantime, here's some information that may help as you continue your Salt journey. Please be sure to review our Code of Conduct. Also, check out some of our community resources including:

• Salt's Contributor Guide
• Join our Community Discord
• Salt Project YouTube channel
• GitHub Discussions

There are lots of ways to get involved in our community. Every month, there are around a dozen opportunities to meet with other contributors and the Salt Core team and collaborate in real time. The best way to keep track is by subscribing to the Salt Community Events Calendar. If you have additional questions, email us at saltproject.pdl@broadcom.com. We're glad you've joined our community and look forward to doing awesome things with you!

Weird, not my first contribution