Update alpine to 3.21.3 from 3.20.3

Release notes https://alpinelinux.org/posts/Alpine-3.21.3-released.html

Author: bump

Dockerfile

@@ -1,6 +1,6 @@
 # bump: alpine /ALPINE_VERSION=alpine:([\d.]+)/ docker:alpine|^3
 # bump: alpine link "Release notes" https://alpinelinux.org/posts/Alpine-$LATEST-released.html
-ARG ALPINE_VERSION=alpine:3.20.3
+ARG ALPINE_VERSION=alpine:3.21.3
 FROM $ALPINE_VERSION AS builder
 
 # Alpine Package Keeper options
@@ -906,7 +906,8 @@ RUN \
   wget $WGET_OPTS -O xavs2.tar.gz "$XAVS2_URL" && \
   echo "$XAVS2_SHA256  xavs2.tar.gz" | sha256sum -c - && \
   tar $TAR_OPTS xavs2.tar.gz && cd xavs2-*/build/linux && \
-  ./configure \
+  # disable all warnings as errors for now
+  CHECK_CFLAGS="-Wno-error" ./configure \
     --disable-asm \
     --enable-pic \
     --disable-cli && \