MAINT: address deprecation warnings in discourse

[lizgehret]

Addresses the following deprecation warnings from discourse:

[lizgehret]

discourse xrefs:
https://meta.discourse.org/t/resolving-the-this-property-fallback-deprecation/337276
https://meta.discourse.org/t/were-upgrading-our-icons-to-font-awesome-6/325349

[lizgehret]

@Oddant1 access that you'll need to complete this (after tests are passing in here):

• Admin access on the forum to:
  • view the warnings above
  • switch the forum into 'read-only' mode
  • initiate a backup
• Access to the caporaso-lab AWS acct to:
  • access the EC2 instance via instance connect

Once you're ready to restart the forum, under EC2 instance connect:

cd /var/discourse
sudo git pull origin main
sudo ./launcher rebuild app

Once that completes successfully, you can go back to the forum, run another backup and then revert the forum from read-only mode.