Fix bad call to tracking_label

What does this MR do?

Fixes error when calling tracking_label when Gitlab::Experimentation.active?(:invite_members_new_dropdown) && can_import_members? is true in this partial

Since the experiment is not active yet in production, there is no impact currently as this evaluates to false.

Updated our tracking issue to wait for this MR to be merged before enabling again - https://gitlab.com/gitlab-org/growth/team-tasks/-/issues/291#note_489158165.

Note we are behind a feature flag/experiment here - as is the bug.

Screenshots (strongly suggested)

error is seen locally

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