chore: Install a newer version of git in the vscode devcontainer to fix failing tests (#9131)

.devcontainer/Dockerfile

@@ -2,6 +2,11 @@ FROM mcr.microsoft.com/vscode/devcontainers/typescript-node:0.157.0-14@sha256:98
 
 # see https://mcr.microsoft.com/v2/vscode/devcontainers/typescript-node/tags/list for tags
 # Add missing Renovate dev tools
-RUN DEBIAN_FRONTEND=noninteractive apt-get update \
+
+# Renovate requires git version 2.22+, while Debian Buster only ships version 2.20.
+# The backports repository contains newer versions of git, which we'll use instead.
+RUN echo 'deb http://deb.debian.org/debian buster-backports main' > /etc/apt/sources.list.d/backports.list \
+   && DEBIAN_FRONTEND=noninteractive apt-get update \
+   && apt-get -y install --no-install-recommends build-essential git/buster-backports \
    && apt-get -y install --no-install-recommends --no-upgrade build-essential \
    && rm -rf /var/lib/apt/lists/*