[PM-6695][PM-6717] Revert Linux build to Ubuntu 20.04 runner (#8289)

* Revert Linux build to Ubuntu 20.04 runner

* Updated notes.

(cherry picked from commit c10a59b)

.github/workflows/build-desktop.yml

@@ -127,7 +127,9 @@ jobs:
     # Note, before updating the ubuntu version of the workflow, ensure the snap base image
     # is equal or greater than the new version. Otherwise there might be GLIBC version issues.
     # The snap base for desktop is defined in `apps/desktop/electron-builder.json`
-    runs-on: ubuntu-22.04
+    # We are currently running on 20.04 until the Ubuntu 24.04 release is available, as moving
+    # to 22.04 now breaks users who are on 20.04 due to mismatched GLIBC versions.
+    runs-on: ubuntu-20.04
     needs: setup
     env:
       _PACKAGE_VERSION: ${{ needs.setup.outputs.package_version }}