⚙️ [Maintenance]: Pin Process-PSModule workflow to v5.4.2

[MariusStorhaug]

This PR pins the Process-PSModule reusable workflow to a specific release version for improved stability and reproducibility.

Summary

• Pinned PSModule/Process-PSModule workflow to commit SHA a15249813c1d7e1a0e4faa2c936fe4978f03845d (v5.4.2)
• Added version comment for easy identification of the pinned version

What's Changed

Workflow Version Pinning

The reusable workflow reference has been updated from a branch reference to a commit SHA:

Before	After
@test/important-file-changes	@a15249813c1d7e1a0e4faa2c936fe4978f03845d (v5.4.2)

Benefits

• Reproducibility: Builds are now deterministic and won't change unexpectedly
• Security: Protects against supply chain attacks via compromised branches
• Stability: Workflow behavior is locked to a known-good release

Upgrade Impact

Impact	Description
Breaking Changes	None
Required Actions	None
Behavior Change	Workflow is now pinned to v5.4.2 instead of following a branch

[github-actions]

No Significant Changes Detected

This PR does not contain changes to files that would trigger a new release:

Path	Description
src/**	Module source code
README.md	Documentation

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