switch to alpine edge, for php8 based composer

.devcontainer/Dockerfile

-FROM alpine:latest
+FROM alpine:edge
 RUN apk update && \
     apk upgrade && \
-    apk add nodejs yarn php8 php8-mysqli php8-mbstring php8-curl git nano composer openssh-client curl && \
+    apk add nodejs yarn php8 php8-mysqli php8-mbstring php8-curl php8-simplexml git nano composer openssh-client curl && \
     curl -L https://unpkg.com/@pnpm/self-installer | node
 
 ENV ENV="/etc/profile"
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