Update canonical/data-platform-workflows action to v20 (#52)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

.github/workflows/ci.yaml

@@ -24,4 +24,4 @@ jobs:
 
   build:
     name: Build rock
-    uses: canonical/data-platform-workflows/.github/workflows/build_rock.yaml@v19.1.0
+    uses: canonical/data-platform-workflows/.github/workflows/build_rock.yaml@v20.0.2

.github/workflows/release.yaml

@@ -15,13 +15,13 @@ on:
 jobs:
   build:
     name: Build rock
-    uses: canonical/data-platform-workflows/.github/workflows/build_rock.yaml@v19.1.0
+    uses: canonical/data-platform-workflows/.github/workflows/build_rock.yaml@v20.0.2
 
   release:
     name: Release rock
     needs:
       - build
-    uses: canonical/data-platform-workflows/.github/workflows/release_rock.yaml@v19.1.0
+    uses: canonical/data-platform-workflows/.github/workflows/release_rock.yaml@v20.0.2
     with:
       artifact-prefix: ${{ needs.build.outputs.artifact-prefix }}
     permissions: