Set strict channel priority

[kenodegard]

Description

For some reason our test environments were installing the following:

pkgs/main::conda-libmamba-solver
conda-forge::libmambapy
conda-forge::libmamba
...

Mixing defaults and conda-forge like this results in ABI conflicts and renders the libmamba solver unusable (see https://github.com/conda/conda-build/actions/runs/10602558349/job/29384860323). To correct this we set the channel priority to strict.

Closes #5468
Closes #5470

Checklist - did you ...

• Add a file to the news directory (using the template) for the next release's release notes?
• Add / update necessary tests?
• Add / update outdated documentation?

[codspeed-hq]

CodSpeed Performance Report

Merging #5469 will not alter performance

_{Comparing kenodegard:strict-priority (c7bd558) with main (a666e34)}

Summary

✅ 3 untouched benchmarks

[jaimergp]

Suggested change

	channel_priority: strict
	channel_priority: strict

This should only apply to the CI step of provisioning base. Otherwise it'll affect all tests.

[jaimergp]

The canary CI should put the conda-canary/label/dev channel first, then followed by defaults. Ideally the dev label should be per-project, like conda_dev. This would prevent other canary projects in the channel (e.g. menuinst) from leaking in there.