Release v2.5.0

[pajlada]

I plan to merge this PR in on Sunday

In the release PR

• [x] Updated version code in src/common/Version.hpp

• [x] Updated version code in CMakeLists.txt
  This can only be "whole versions", so if you're releasing 2.4.0-beta you'll need to condense it to 2.4.0

• [x] Add a new release at the top of the releases key in resources/com.chatterino.chatterino.appdata.xml
  This cannot use dash to denote a pre-release identifier, you have to use a tilde instead.

• [x] Updated version code in .CI/chatterino-installer.iss
  This can only be "whole versions", so if you're releasing 2.4.0-beta you'll need to condense it to 2.4.0

• [x] Update the changelog ## Unreleased section to the new version CHANGELOG.md
  Make sure to leave the ## Unreleased line unchanged for easier merges

After the PR has been merged

• [ ] Tag the release
• [ ] Manually run the create-installer workflow.
  This is only necessary if the tag was created after the CI in the main branch finished.
• [x] Start a manual Launchpad import - scroll down & click Import Now
• [x] Make a PPA release to this repo with the debchange command.
  debchange -v 2.4.0 then add the changelog entries
  debchange --release then change the distro to be unstable