Travis: always build docbooks

This ensures the builds remain broken if the docbook build fails and a
subsequent commit not affecting the docbook is successful.

Fixes #20471

scripts/travis_script.sh

@@ -9,28 +9,15 @@
 #
 function build_docbook() {
 
-	# Get the list of modified docbooks from the commit range
-	UPDATED_DOCBOOKS=$(
-		git diff --name-only $TRAVIS_COMMIT_RANGE -- docbook/ |
-		grep -i '\.xml$' |
-		cut -d '/' -f 2 |
-		sort -u
-	)
+	DOCBOOKS="Admin_Guide Developers_Guide"
 
-	# Build the docbook if any XML files have been updated
-	if [[ -n $UPDATED_DOCBOOKS ]]
-	then
-		# Build the books
-		for BOOK in $UPDATED_DOCBOOKS
-		do
-			echo
-			echo "Building '$BOOK'..."
-			cd $TRAVIS_BUILD_DIR/docbook/$BOOK
-			make
-		done
-	else
-		echo "No documentation changes in $TRAVIS_COMMIT_RANGE"
-	fi
+	for BOOK in $DOCBOOKS
+	do
+		echo
+		echo "Building '$BOOK'..."
+		cd $TRAVIS_BUILD_DIR/docbook/$BOOK
+		make
+	done
 }