add a commonly used virtualenv directory as a sample path to exclude

What does this MR do?

Add */venv/* as a second example path to exclude for the SAST_BANDIT_EXCLUDED_PATHS variable.

• Virtual environments like virtualenv are commonly used in Python for uses like testing and packaging. A common path used for virtual environments is venv.
• The Python .gitlab-ci.yml template includes the use of venv
• Enabling the bandit SAST scan on a Python project with virtualenv results in over 2000 vulnerabilities from the venv path alone, creating a large number of confusing false positives

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Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team