ci: fix exclude path format pymarkdownlnt

Signed-off-by: Anne Chew <anne.chew@canonical.com>

Author: AnneCYH

docs/Makefile

@@ -110,7 +110,7 @@ pa11y: pa11y-install html
 	find $(BUILDDIR) -name *.html -print0 | xargs -n 1 -0 $(PA11Y)
 
 lint-md: pymarkdownlnt-install
-	@. $(VENV); pymarkdownlnt --config $(SPHINXDIR)/.pymarkdown.json scan --recurse --exclude=./$(SPHINXDIR)/** $(SOURCEDIR)
+	@. $(VENV); pymarkdownlnt --config $(SPHINXDIR)/.pymarkdown.json scan --recurse --exclude=$(SPHINXDIR) $(SOURCEDIR)
 
 vale-install: install
 	@. $(VENV); test -f $(VALE_CONFIG) || python3 $(SPHINXDIR)/get_vale_conf.py