CI: Fix build on Ubuntu<=24

* .github/workflows/build.yml: Update `Install mu4e' job to work with
Ubuntu-22 sources list format as well.

.github/workflows/build.yml

@@ -31,7 +31,13 @@ jobs:
       - name: Install mu4e
         run: |
           emacs=`which emacs`
+
+          # Ubuntu<24
+          test -e /etc/apt/sources.list && \
+            sudo sed -i '/^deb/P;s/^deb/deb-src/' /etc/apt/sources.list
+          # Ubuntu>=24
           sudo sed -i 's/^Types: deb/Types: deb deb-src/' /etc/apt/sources.list.d/*
+
           sudo apt-get update
           sudo apt-get install git meson emacs
           sudo apt-get build-dep maildir-utils