chore: drop support for Ubuntu 20.04

This is no longer supported upstream by Canonical.

contrib/release-dokku

@@ -144,7 +144,7 @@ fn-publish-package() {
       fi
     done
   elif [[ "$DIST" == "ubuntu" ]]; then
-    OS_IDS=("focal" "jammy" "noble")
+    OS_IDS=("jammy" "noble")
     for OS_ID in "${OS_IDS[@]}"; do
       log-info "(release-dokku) pushing ${RELEASE_TYPE} to packagecloud.com/${REPOSITORY}/${DIST}"
       package_cloud push "${REPOSITORY}/${DIST}/${OS_ID}" "$PACKAGE_NAME"