build: print current Git ref at the top of the build transcript

[cfm]

Status

Ready for review

Description of Changes

Closes #6792 by prefacing the script transcript logged by make-build-debs.sh with the output of git log -1 --oneline, e.g.:

user@sd-dev:~/securedrop$ head build/20231019-securedrop.log
Script started on 2023-10-19 18:19:19-07:00 [TERM="xterm-256color" TTY="/dev/pts/4" COLUMNS="104" LINES="54"]
+ git log -1 --oneline
53f8dea23 (HEAD -> 6792-print-git-ref, origin/develop, origin/HEAD, develop) gpg: Signature made Thu 19 Oct 2023 01:24:00 PM PDT
gpg:                using RSA key 4AEE18F83AFDEB23
gpg: Can't check signature: No public key
Merge pull request #6830 from freedomofpress/ansible-major-bump
++ pwd
+ OCI_RUN_ARGUMENTS='--user=root -v /home/user/securedrop:/src:Z'
+ which podman
+ OCI_BIN=podman

Testing

• Visual review.

Deployment

Tooling-only; no deployment considerations. May be worth backporting into release/2.7.0 to increase the usefulness of our build logs.

[legoktm]

Super simple and works as expected, except it's outputting color codes :( Suggestion to fix that inline!

[legoktm]

Perfect :)