chore(deps): update dependency helm to v3.21.0

| datasource      | package   | from   | to      |
| --------------- | --------- | ------ | ------- |
| github-releases | helm/helm | v3.8.1 | v3.21.0 |

Author: renovate[bot]

.github/workflows/lint-test.yaml

@@ -17,7 +17,7 @@ jobs:
       - name: Set up Helm
         uses: azure/setup-helm@1a275c3b69536ee54be43f2070a358922e12c8d4 # v4
         with:
-          version: v3.8.1
+          version: v3.21.0
 
       # Python is required because `ct lint` runs Yamale (https://github.com/23andMe/Yamale) and
       # yamllint (https://github.com/adrienverge/yamllint) which require Python

.github/workflows/release.yaml

@@ -26,7 +26,7 @@ jobs:
       - name: Install Helm
         uses: azure/setup-helm@v4
         with:
-          version: v3.8.1
+          version: v3.21.0
 
       # Optional step if GPG signing is used
       - name: Prepare GPG key