Makefile: make validate-epub check v2 output too.

See #9469.

Makefile

@@ -255,10 +255,13 @@ validate-epub: ## generate an epub and validate it with epubcheck and ace
 	which epubcheck || exit 1
 	which ace || exit 1
 	tmp=$$(mktemp -d) && \
-	$(pandoc) test/epub/wasteland.native -Mtitle="The Wasteland" --resource-path test/epub -o $$tmp/file.epub --number-sections --toc --quiet && \
-	echo $$tmp/file.epub && \
-	epubcheck $$tmp/file.epub && \
-	ace $$tmp/file.epub -o ace --force
+  for epubver in 2 3; do \
+  file=$$tmp/ver$$epubver.epub ; \
+	$(pandoc) test/epub/wasteland.native -Mtitle="The Wasteland" --resource-path test/epub -t epub$$epubver -o $$file --number-sections --toc --quiet && \
+	echo $$file && \
+	epubcheck $$file || exit 1 && \
+	ace $$file -o ace-report-v$$epubver --force ; \
+  done
 
 modules.csv: $(PANDOCSOURCEFILES)
 	@rg '^import.*Text\.Pandoc\.' --with-filename $^ \