Update keyserver to keys.openpgp.org for comms key

[eloquence]

Status

Ready for review

Description of Changes

Part of #4128

Testing

• Use a virtualized Tails env or a prod-like setup to test this PR.
• Remove the securedrop@freedom.press key from your keyring
• Run the securedrop-admin logs playbook from this branch and verify that the key is successfully imported and the logs are encrypted to the comms key

Deployment

This is important mitigation against cert flooding attacks, so admins should be encouraged to update their workstations to pick up this fix

Checklist

• I have followed my own test plan

[codecov-io]

Codecov Report

Merging #4576 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff            @@
##           develop    #4576   +/-   ##
========================================
  Coverage    82.53%   82.53%           
========================================
  Files           45       45           
  Lines         3121     3121           
  Branches       339      339           
========================================
  Hits          2576     2576           
  Misses         458      458           
  Partials        87       87

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[emkll]

Thanks @eloquence, works as expected in Tails: the key is imported and the logs are encrypted to the correct key.