Bump actions/download-artifact from v2 to v2

Author: renovate-pagopa[bot]

.github/workflows/ci.yml

@@ -100,7 +100,7 @@ jobs:
           key: ${{ runner.os }}-sbt-cache-v2-${{ hashFiles('**/*.sbt') }}-${{ hashFiles('project/build.properties') }}
 
       - name: Download target directories (2.13.10)
-        uses: actions/download-artifact@v2
+        uses: actions/download-artifact@cbed621e49e4c01b044d60f6c80ea4ed6328b281 # v2
         with:
           name: target-${{ matrix.os }}-2.13.10-${{ matrix.java }}