[INFRA] LGTM alert

[DimitriPapadopoulos]

I tried to work around an LGTM alert with bb6065a in #853. Unfortunately, this doesn't work:
https://lgtm.com/projects/g/bids-standard/bids-specification/snapshot/56824aa6b869bcbec1fb14c50e3771cfc0358af5/files/pdf_build_src/process_markdowns.py?sort=name&dir=ASC&mode=heatmap#xea83c650d9db5491:1

I believe LGTM wants a lone noqa comment. If so, we need to change:

from schemacode import macros # noqa (used in "eval" call later on)

into:

# used in "eval" call later on
from schemacode import macros  # noqa

or, although I know you don't like it::

# used in "eval" call later on
from schemacode import macros  # noqa: F417 lgtm [py/unused-import]

Last option, we could even revert to:

# used in "eval" call later on
from schemacode import macros  # noqa: F417

and disable the relevant LGTM alert globally using an lgtm.yml configuration file.

Which of these three options do you prefer? I prefer option 3, as LGTM is raising a false positive that cannot be worked around without sacrificing code quality (see github/codeql#6517).