set group id explicitly

Dockerfile

@@ -17,7 +17,7 @@ FROM python:3-alpine
 
 WORKDIR /app
 
-RUN addgroup radicale \
+RUN addgroup -g 1000 radicale \
     && adduser radicale --home /var/lib/radicale --system --uid 1000 --disabled-password -G radicale \
     && apk add --no-cache ca-certificates openssl
 

Dockerfile.dev

@@ -15,7 +15,7 @@ FROM python:3-alpine
 
 WORKDIR /app
 
-RUN addgroup radicale \
+RUN addgroup -g 1000 radicale \
     && adduser radicale --home /var/lib/radicale --system --uid 1000 --disabled-password -G radicale \
     && apk add --no-cache ca-certificates openssl