fix(ci): resolve the helm dependencies with dependency update

`helm dependency build` only downloads charts from repositories that are already registered in the local repository
cache. On a fresh runner that cache is empty, so the classic repository of the valkey dependency could not be resolved:
"no repository definition for https://valkey.io/valkey-helm. Please add the missing repos via 'helm repo add'". The two
bitnami dependencies were unaffected, because OCI references do not need a repository entry.

`helm dependency update` resolves the repository URLs straight from `Chart.yaml` and therefore needs no additional
`helm repo add` step. Repeating the URL in the workflow would only invite drift, since renovate updates `Chart.yaml`
alone. All three dependencies are pinned to exact versions, so the resolution result is identical to `Chart.lock`.

This corrects 0102563, which introduced the `dependency build` step.

Co-authored-by: Copilot <copilot@github.com>

.gitea/workflows/helm.yaml

@@ -18,8 +18,8 @@ jobs:
     - uses: azure/setup-helm@9bc31f4ebc9c6b171d7bfbaa5d006ae7abdb4310 # v5.0.1
       with:
         version: v4.3.0 # renovate: datasource=github-releases depName=helm/helm
-    - name: Build helm dependencies
-      run: helm dependency build
+    - name: Update helm dependencies
+      run: helm dependency update
     - name: Lint helm files
       run: |
         helm lint --values values.yaml .
@@ -35,7 +35,7 @@ jobs:
         HELM_UNITTEST_VERSION: v1.0.0 #renovate: datasource=github-releases depName=helm-unittest/helm-unittest
       name: Install helm-unittest
       run: helm plugin install --verify=false --version "${HELM_UNITTEST_VERSION}" https://github.com/helm-unittest/helm-unittest
-    - name: Build helm dependencies
-      run: helm dependency build
+    - name: Update helm dependencies
+      run: helm dependency update
     - name: Execute helm unittests
       run: helm unittest --strict --file 'unittests/**/*.yaml' .