docs-requirements: fix warning with remoulade > 5 (#4466)

This warns locally because `RateLimitEnqueue` has been moved to an
optional package:

sphinx.errors.SphinxWarning: autodoc: failed to import module 'remoulade' from module 'opentelemetry.instrumentation'; the following exception was raised:
cannot import name 'RateLimitEnqueue' from 'remoulade.rate_limits' (/home/rm/src/opentelemetry-python-contrib/.tox/docs/lib/python3.12/site-packages/remoulade/rate_limits/__init__.py)