Fix: revision in CI Docker image

[aldur]

Description

The Dockerfile we are using in CI prevented the build.rs file from getting the current git_commit, which was resulting in an empty revision (e.g. in metrics, this was also breaking Cloudwatch collection).

(For context, this took me longer than I expected because the code did not check the result of git rev-parse and would produce an empty string on failure).

This fixes it.

Before merging, please that the build resulting from this manual run embeds the correct revision.

[matteojug]

Tested locally, devenv local and devenv pulling the built image from CI and got a revision in all of them. CI one:

starting the sBTC signer rust_version="rustc 1.80.0 (051478957 2024-07-21)" revision="fix/revision_in_docker_image" arch="x86_64" env_abi="gnu"