Test Emacs 27.2 on Ubuntu in CI

27.1 is the declared floor, so cover it in CI again.  It was dropped
because MELPA's flycheck HEAD requires Emacs 28.1 and would not install on
27; the previous commit's Eask.27 pulls 27's dependencies from MELPA
Stable instead, which supports it.

Ubuntu only: one platform is enough to catch a 27-specific break, and it
keeps the matrix small.

Author: zonuexe

.github/workflows/test.yml

@@ -24,6 +24,12 @@ jobs:
           - 30.1
         experimental: [false]
         include:
+        # Emacs 27.1 is the declared floor.  Run it on Ubuntu only: its
+        # dependencies come from MELPA Stable via Eask.27 (MELPA's HEAD needs
+        # Emacs 28.1), and one platform is enough to catch a 27-specific break.
+        - os: ubuntu-latest
+          emacs-version: "27.2"
+          experimental: false
         - os: ubuntu-latest
           emacs-version: snapshot
           experimental: true