⚙️ [Maintenance]: Workflow reference pinned to immutable SHA (#575)

The CI workflow reference is now pinned to a specific commit SHA,
consistent with all other `uses:` references in the PSModule
infrastructure. Dependabot will automatically propose updates when new
versions of Process-PSModule are released.

- Fixes #574

## Changed: Workflow reference pinned to immutable SHA

The `Process-PSModule` reusable workflow reference in
`.github/workflows/Process-PSModule.yml` was using a mutable major
version tag (`@v5`). It is now pinned to the exact commit SHA with the
patch-level version in a trailing comment:

```yaml
# Before
uses: PSModule/Process-PSModule/.github/workflows/workflow.yml@v5

# After
uses: PSModule/Process-PSModule@4343d76 # v5.4.5
```

Dependabot's `github-actions` ecosystem is already configured and will
keep this reference up to date automatically.

## Technical Details

- Changed `@v5` to `@4343d76f9e8c9468527175ea292092c2d055be8c # v5.4.5`
in `.github/workflows/Process-PSModule.yml`.
- The existing `dependabot.yml` already covers `github-actions` in `/`,
so SHA-pinned reusable workflow references will be updated
automatically.
- No functional change — `v5` currently resolves to the same commit
(`4343d76`).

Author: MariusStorhaug

.github/workflows/Process-PSModule.yml

@@ -27,5 +27,5 @@ permissions:
 
 jobs:
   Process-PSModule:
-    uses: PSModule/Process-PSModule/.github/workflows/workflow.yml@v5
+    uses: PSModule/Process-PSModule/.github/workflows/workflow.yml@4343d76f9e8c9468527175ea292092c2d055be8c # v5.4.5
     secrets: inherit