chore(deps): update docker.io/library/alpine docker tag to v3.21.0

Dockerfile

@@ -1,5 +1,5 @@
 # NOTE: also update the renovate comment below if you change the minor version!
-FROM docker.io/library/alpine:3.20.3@sha256:1e42bbe2508154c9126d48c2b8a75420c3544343bf86fd041fb7527e017a4b4a
+FROM docker.io/library/alpine:3.21.0@sha256:e323a465c03a31ad04374fc7239144d0fd4e2b92da6e3e0655580476d3a84621
 
 # renovate: datasource=repology depName=alpine_3_20/clamav versioning=loose
 ENV CLAMAV_VERSION="1.2.2-r0"