ci: add basic checks for CHANGELOG.md

Perform some basic checks for CHANGELOG.md.

In particular, check for
 - missing periods;
 - extra spaces at EOL;
 - non-ASCII characters.

Fix the issues found.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

.github/workflows/validate.yml

@@ -157,7 +157,6 @@ jobs:
           pattern: '^.{0,72}(\n.*)*$'
           error: 'Subject too long (max 72)'
 
-
   cfmt:
     runs-on: ubuntu-20.04
     steps:
@@ -182,6 +181,10 @@ jobs:
       uses: actions/checkout@v3
       with:
         fetch-depth: 0
+
+    - name: check CHANGELOG.md
+      run: make verify-changelog
+
       # We have to run this under Docker as Ubuntu (host) does not support all
       # the architectures we want to compile test against, and Dockerfile uses
       # Debian (which does).