chore(deps): update alpine docker tag to v3.21

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

Author: renovate[bot]

.github/actions/tools/Dockerfile

@@ -12,7 +12,7 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-FROM alpine:3.19
+FROM alpine:3.21
 
 LABEL maintainer="Nicolas Lamirault <[email protected]>" \
     org.opencontainers.image.title="Tools for Portefaix project" \