If PDF file is too small, return error; add workaround for problematic warning

When generating PDF of the docs site, if a warning admonition spreads
from one page to the next one, pdf conversion silently crashes.
After pdf generation, let's check the PDF file size.

As a short-term workaround in our documentation,
let's split the problematic warning admonition in two paragraphs.

Author: badlop

.github/workflows/ci.yml

@@ -38,6 +38,7 @@ jobs:
                          beautifulsoup4
       - run: make home
       - run: make pdf
+      - run: make pdf-test
       - run: make zip
       #- run: make test
       - run: mkdocs gh-deploy --force

Makefile

@@ -34,6 +34,7 @@ TAGS=content/developer/ejabberd-api/admin-tags.md
 PDFNAME=ejabberd-docs-$(VERSION).pdf
 PDF=content/ejabberd-docs.pdf
 PDFV=content/$(PDFNAME)
+PDF_SIZE=$(shell stat -c %s $(PDFV))
 
 ZIPNAME=ejabberd-docs-$(VERSION).zip
 ZIP=content/ejabberd-docs.zip
@@ -55,6 +56,7 @@ help:
 	@echo ""
 	@echo "  site     Generate site as HTML files"
 	@echo "  pdf      Generate PDF file of the offline site"
+	@echo "  pdf-test Test the PDF file size (more than 3MB)"
 	@echo "  zip      Generate ZIP file of the offline site"
 	@echo ""
 	@echo "  serve    Start MkDocs web server"
@@ -300,12 +302,15 @@ site:
 	OFFLINE=true mkdocs build
 	find site/* -type f \! -exec sed -i 's/href="\(.*\)" \(title="ejabberd Docs"\)/href="\1\/index.html" \2/g' {} \;
 
-pdf: $(PDF)
+pdf: $(PDFV)
 
-$(PDF):
+$(PDFV):
 	WITH_PDF=1 mkdocs build
 	mv $(PDF) $(PDFV)
 
+pdf-test: $(PDFV)
+	[ $(PDF_SIZE) -gt 3000000 ] || exit 1
+
 zip: $(ZIP)
 
 $(ZIP): site

content/admin/configuration/modules.md

@@ -3134,7 +3134,11 @@ identity verification based on DNS.
 
     DNS-based verification is vulnerable to [DNS cache
     poisoning](https://en.wikipedia.org/wiki/DNS_spoofing), so modern
-    servers rely on verification based on PKIX certificates. Thus this
+    servers rely on verification based on PKIX certificates.
+
+!!! warning
+
+    This
     module is only recommended for backward compatibility with servers
     running outdated software or non-TLS servers, or those with invalid
     certificates (as long as you accept the risks, e.g. you assume that