Upgrade pycparser to 2.21 in all requirements files

[audiodude]

Status

Ready for review

Description of Changes

Fixes #6618

Changes proposed in this pull request:

Upgrade of pycparser library.

Testing

Tested with make test.

Deployment

Any special considerations for deployment? Consider both:

1. Upgrading existing production instances.

Not sure how production instances receive updates from requirements files.

3. New installs.

Should be fine.

Checklist

If you made changes to the server application code:

• Linting (make lint) and tests (make test) pass in the development container

If you made changes to securedrop-admin:

• Linting and tests (make -C admin test) pass in the admin development container

If you made changes to the system configuration:

• [?] Configuration tests pass

If you added or removed a file deployed with the application:

N/A

If you made non-trivial code changes:

N/A

Choose one of the following:

• I have opened a PR in the docs repo for these changes, or will do so later
• I would appreciate help with the documentation
• These changes do not require documentation

If you added or updated a production code dependency:

Production code dependencies are defined in:

• admin/requirements.in
• admin/requirements-ansible.in
• securedrop/requirements/python3/securedrop-app-code-requirements.in

If you changed another requirements.in file that applies only to development
or testing environments, then no diff review is required, and you can skip
(remove) this section.

Choose one of the following:

• I have performed a diff review and pasted the contents to the packaging wiki
• I would like someone else to do the diff review

[nathandyer]

Tested locally using make-dev, verified I could create and log into a journalist account. Diff review is approved. This should be in a mergeable state.