monopam tests: shorten long identifier names (E320)
Trim 5–6-underscore test function names down to ≤4 segments. The
alcotest description string keeps the full intent; only the OCaml
identifier shrinks. No test logic changed.
Examples: test_derive_sources_override_branch_from_dune ->
test_derive_override_branch_dune; test_normalize_url_strips_dot_git ->
test_normalize_url_strip_dotgit; test_pp_subtree_info_with_commit ->
test_pp_subtree_with_commit.