snmp_security_check plugin lacks test

[ericwb]

Describe the bug

Each plugin should be exercising a test to ensure it works build to build. The newly introduced snmp_security_check
has https://github.com/PyCQA/bandit/blob/master/examples/snmp.py, but the test_functional.py isn't running on it.

Reproduction steps

1. View tests/functional/test_functional.py
2. Search on "snmp"
3. Notice no testing of snmp_security_check

Expected behavior

Every plugin needs to run a functional test to ensure its quality.

Bandit version

1.7.2 (Default)

Python version

3.9

Additional context

No response