ci: pin Process-PSModule to commit SHA

Per the GitHub Actions coding standard, uses: references are pinned to a full 40-character commit SHA with the human-readable version as a trailing comment. Replaces the v6.1.2 tag pin with its commit SHA (d4020f3).

Author: MariusStorhaug

.github/workflows/Process-PSModule.yml

@@ -27,7 +27,7 @@ permissions:
 
 jobs:
   Process-PSModule:
-    uses: PSModule/Process-PSModule/.github/workflows/workflow.yml@v6.1.2
+    uses: PSModule/Process-PSModule/.github/workflows/workflow.yml@d4020f3c9c3621cebae5d8bf4ffaf10f55c1784a # v6.1.2
     secrets:
       APIKey: ${{ secrets.APIKey }}
       # E2E: push a secret (masked in logs) and a variable (not masked) into the module test jobs.