Ensure absence of img tags

.github/workflows/lint.yml

@@ -60,6 +60,24 @@ jobs:
 
           exit $rc
 
+      - name: Verify absence of <img> tags
+        run: |
+          function err {
+            >&2 echo -e "\033[0;31m$@\033[0m"
+          }
+
+          rc=0
+
+          while read -r file; do
+            echo "Checking $file"
+
+            if grep -q "<img" "$file"; then
+              err "$file contains forbidden <img> tags. Use AsciiDoc image macros instead."
+            fi
+          done < <(find . -type f -name "*.adoc")
+
+          exit $rc
+
   drawio:
     runs-on: ubuntu-latest
 
@@ -105,7 +123,7 @@ jobs:
             echo "Checking $file"
 
             if grep -qE "^@startuml\s+." "$file"; then
-              err "$file contains illegal output name in @startuml"
+              err "$file contains forbidden output name in @startuml"
               rc=1
             fi
           done < <(find . -name "*.puml")