fix(deps): replace step-security/retry and update action pins (#468)

* fix(deps): replace step-security/retry with nick-fields/retry

* chore(deps): update github action sha pins via pinact

* refactor: remove common-retry references from tests and validators

* chore: simplify description fallback and update action count

* docs: remove hardcoded test counts from memory and docs

Replace exact "769 tests" references with qualitative language
so these files don't go stale as test count grows.

csharp-build/action.yml

@@ -155,7 +155,7 @@ runs:
         cache-dependency-path: '**/packages.lock.json'
 
     - name: Restore Dependencies
-      uses: step-security/retry@e1d59ce1f574b32f0915e3a8df055cfe9f99be5d # v3.0.4
+      uses: nick-fields/retry@ce71cc2ab81d554ebbe88c79ab5975992d79ba08 # v3.0.2
       with:
         timeout_minutes: 10
         max_attempts: ${{ inputs.max-retries }}
@@ -203,7 +203,7 @@ runs:
 
     - name: Upload Test Results
       if: always()
-      uses: actions/upload-artifact@b7c566a772e6b6bfb58ed0dc250532a479d7789f # v6.0.0
+      uses: actions/upload-artifact@bbbca2ddaa5d8feaa63e36b76fdaad77386f024f # v7.0.0
       with:
         name: csharp-test-results
         path: |