Reproducibility issue linked to different length of commits under HEADS_GIT_VERSION

[tlaurion]

There is a difference between git reports of what is specified in Makefile to obtain git tag+commit: HEADS_GIT_VERSION := $(shell git describe --tags --dirty)

osresearch:
v0.2.0-1263-gf2e45c4

tlaurion:
v0.2.0-1263-gf2e45c43

Note the difference in length, being 7 or 8 characters above

Seems like the way to fix this would be to set the abbrev option to fixate length of commit length output:
--abbrev[=<n>] use <n> digits to display object names

Github shows commit ids in an abbrev form of 7 characters. We should force the same inside of the builds for consistency and to avoid reproducibility issues on that:
HEADS_GIT_VERSION := $(shell git describe --tags --abbrev=7 --dirty)

Locally, this fixes the issue:

user@heads-tests:~/heads$ git describe --tags --abbrev=7 --dirty
v0.2.1.bis2-144-gf2e45c4-dirty
user@heads-tests:~/heads$ git describe --tags --dirty
v0.2.1.bis2-144-gf2e45c43-dirty

Originally posted by @tlaurion in #1225 (comment)