Update Dockerfile (Azure#19096)

* Update Dockerfile

* use ubuntu20.04

Author: ruowan

scripts/datacontainer/Dockerfile

@@ -1,9 +1,7 @@
-FROM mcr.microsoft.com/cbl-mariner/distroless/base:1.0
-
-RUN apk update && \
-    apk add git
+FROM mcr.microsoft.com/oss/mirror/docker.io/library/ubuntu:20.04
 
 RUN mkdir -p /usr/data/specrepo/
+
 COPY .git /usr/data/specrepo/.git
 
 WORKDIR /usr/data/scripts/