update ubuntu build to install git from jammy default repo

Signed-off-by: Rui Yang <ruiya@vmware.com>

README.md

@@ -369,7 +369,8 @@ Run the tests with the following commands for both `alpine` and `ubuntu` images:
 
 ```sh
 docker build -t git-resource --target tests -f dockerfiles/alpine/Dockerfile .
-docker build -t git-resource --target tests -f dockerfiles/ubuntu/Dockerfile .
+docker build -t registry-image-resource --target tests -f dockerfiles/ubuntu/Dockerfile --build-arg base_image=ubuntu:latest .
+
 ```
 
 #### Note about the integration tests

dockerfiles/ubuntu/Dockerfile

@@ -1,10 +1,12 @@
-ARG base_image=ubuntu:bionic
+ARG base_image
 
 FROM ${base_image} AS resource
 
 RUN apt update && apt upgrade -y -o Dpkg::Options::="--force-confdef"
 RUN apt install -y --no-install-recommends \
     curl \
+    git \
+    git-lfs \
     gnupg \
     gzip \
     jq \
@@ -16,14 +18,6 @@ RUN apt install -y --no-install-recommends \
     libstdc++6 \
     software-properties-common
 
-RUN apt-add-repository ppa:git-core/ppa \
-  && apt update \
-  && apt install -y git \
-  && rm -rf /var/lib/apt/lists/*
-
-RUN curl -s https://packagecloud.io/install/repositories/github/git-lfs/script.deb.sh | bash
-RUN apt install -y git-lfs
-
 WORKDIR /root
 RUN git clone https://github.com/proxytunnel/proxytunnel.git && \
     cd proxytunnel && \