avoid useless fomantic rebuilds (#9999)

the `fomantic` target for some reason does sometimes not update the
timestamp on the directory, leading to useless rebuild. Manually update
the timestamp at the end of the build to avoid this and also added the
same to js/css targets.

Makefile

 $(JS_DEST): $(JS_SOURCES) | node_modules
 	npx eslint web_src/js webpack.config.js
 	npx webpack --hide-modules --display-entrypoints=false
+	@touch $(JS_DEST)
 
 .PHONY: fomantic
 fomantic: node-check $(FOMANTIC_DEST_DIR)
 	cp web_src/fomantic/theme.config.less node_modules/fomantic-ui/src/theme.config
 	cp web_src/fomantic/_site/globals/* node_modules/fomantic-ui/src/_site/globals/
 	npx gulp -f node_modules/fomantic-ui/gulpfile.js build
+	@touch $(FOMANTIC_DEST_DIR)
 
 .PHONY: css
 css: node-check $(CSS_DEST)
 	npx lessc web_src/less/index.less public/css/index.css
 	$(foreach file, $(filter-out web_src/less/themes/_base.less, $(wildcard web_src/less/themes/*)),npx lessc web_src/less/themes/$(notdir $(file)) > public/css/theme-$(notdir $(call strip-suffix,$(file))).css;)
 	npx postcss --use autoprefixer --use cssnano --no-map --replace public/css/*
+	@touch $(CSS_DEST)
 
 .PHONY: update-translations
 update-translations: