Restore dropped virtualenv activation in securedrop-admin

[rmol]

Status

Ready for review

Description of Changes

Fixes #4920.

Restores dropped virtualenv activation in securedrop-admin.

Testing

Follow the STR in #4920. The last step (raging) should not be required.

Deployment

Fixes securedrop-admin.

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 non-trivial code changes:

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

[emkll]

Thanks @rmol for the quick fix. Tested as follows:

Tails 3.16 -> 4.0-rc1

Ran the install scripts against prod vms:

• ran./securedrop-admin install, observed admin/.venv3 deleted, prompted to run ./securedrop-admin setup
• ./securedrop-admin sdconfig completes successfully
• ./securedrop-admin setup completes successfully
• ./securedrop-admin install completes successfully
• ./securedrop-admin tailsconfig completes successfully (and the desktop shortcuts are functional)
• ./securedrop-admin backup completes successfully.

Fresh Tails 4.0-rc1 install

Note: did not run to completion due to lack of hardware available at this time, but ensured Ansible was invoked):

• ./securedrop-admin setup completes successfully
• ./securedrop-admin sdconfig completes successfully
• ./securedrop-admin install invokes ansible (but fails due to instance config)
• ./securedrop-admin tailsconfig invokes ansible (but fails due to lack of instance config)
• ./securedrop-admin backup invokes ansible (but fails due to lack of instance config)

Good to merge when CI passes.

[emkll]

I am getting an issue with the securedrop GUI updater on this branch (attempting to "upgrade" to 1.0.0):

ERROR: Failed to install pip dependencies. Check network connection and try again.
Update failed. Please contact your SecureDrop administrator.

I think this is unrelated to this PR, but maybe is Tails4-specific?

EDIT: Definitely not related to this PR. Checked out 1.1.0-rc1 and disabled/re-enabled the network, the same issue occurs. This happens after 1.0.0 is checked out, and might be due to tails-4 compatibility not being present in 1.0.0

[emkll]

The updater issue raised in #4921 (comment) is unrelated, it should only pose an issue when upgrading to a SecureDrop version with no Tails 4 support (which shouldn't happen under normal circumstances, once 1.1.0 is released. Merging!