docs: avoid concurrency issues when generating images in parallel

docs/source/_images/Makefile

@@ -1,4 +1,4 @@
-all: examples all_tex tidy
+all: examples all_tex
 
 # set a fake time in pdf generation to prevent unnecessary differences in output
 FAKETIME := TZ='Z' faketime -f '2022-01-01 00:00:00 x0,001'
@@ -31,14 +31,13 @@ all_tex: $(TEX_FILES:.tex=.pdf) $(TEX_FILES:.tex=.svg)
 
 %.pdf: %.tex
 	cd $(@D) && $(FAKETIME) pdflatex $(<F) --interaction=nonstopmode
+	rm -f $(*).aux $(*).log
 
 %.svg: %.pdf
 	pdf2svg $< $@
 
-.PHONY: clean tidy
-tidy:
-	rm -f  **/*.log **/*.aux
+.PHONY: clean
 
-clean: tidy
+clean:
 	rm -rf code_examples
 	rm -f **/*.pdf **/*.svg