Update cryptography to 3.4.7 in dev reqs too

[rmol]

Status

Ready for review

Description of Changes

This updates cryptography to 3.4.7 in the development requirements too.

Testing

• CI is green.
• make venv produces a virtualenv containing cryptography 3.4.7.
• The fpf-www-projects safety checks stop warning about the use of cryptography 3.2.1.

Deployment

Dev only.

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 non-trivial code changes:

• I have written a test plan and validated it for this PR

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 code dependency:

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
• the dependency was already reviewed, in Fixes #5898 Adds latest cryptography #5964

[rmol]

To get past the lint error, this will need to be rebased after #5977 is merged.

[kushaldas]

sha256sum matched.