Set the dependabot_updater_version docker env from the build arg

[Nishnha]

Fixes #8885 (comment) where our sentry releases are still reporting the default value of "development" instead of the build SHA.

We were passing in the DEPENDABOT_UPDATER_VERSION env as a build arg but referencing it as an ENV in docker https://docs.docker.com/reference/cli/docker/container/run/#env

Docker buildx doesn't support the --env flag, but we can still pass the variable in as a build arg and then use it to set a docker environment variable

[jurre]

How can we verify that this change resolves the issue @Nishnha ?

[Nishnha]

How can we verify that this change resolves the issue @Nishnha ?

We should be able to check what the value of $DEPENDABOT_UPDATER_IMAGE is on an image build from this branch.
We should also start seeing the correct release values in sentry

I also realized that docker buildx doesn't support the --env flag, but we can still pass the variable in as a build arg and then use it to set a docker environment variable
https://docs.docker.com/reference/cli/docker/buildx/build/

I'll update this PR to do that.

[Nishnha]

This looks right!

I pulled the build image and ran docker inspect on it

$ docker pull ghcr.io/dependabot/dependabot-updater-bundler:44819e7652f0f213e0129c25509a6bfeb1dc5e53
$ docker images

REPOSITORY                                                               TAG                                        IMAGE ID       CREATED          SIZE
ghcr.io/dependabot/dependabot-updater-bundler                            44819e7652f0f213e0129c25509a6bfeb1dc5e53   ef0479026bcd   17 minutes ago   724MB

$ docker inspect ef0479026bcd 

"Env": [
  "PATH=/home/dependabot/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin",
  "DEBIAN_FRONTEND=noninteractive",
  "LC_ALL=en_US.UTF-8",
  "LANG=en_US.UTF-8",
  "DEPENDABOT_HOME=/home/dependabot",
  "DEPENDABOT=true",
  "GIT_LFS_SKIP_SMUDGE=1",
  "DEPENDABOT_NATIVE_HELPERS_PATH=/opt",
  "DEPENDABOT_UPDATER_VERSION=44819e7652f0f213e0129c25509a6bfeb1dc5e53"
],

[Nishnha]

That worked!