MNT Check only selected directories with ruff (#1446)

In PR #1421, ruff was extended to check all directories. This is fine
for those directories that come with PEFT. However, developers may have
other local directories that they do not want to be checked. Therefore,
it is better to list the directories to be checked rather than checking
all.

Makefile

@@ -1,6 +1,6 @@
 .PHONY: quality style test docs
 
-check_dirs := .
+check_dirs := src tests examples docs scripts docker
 
 # Check that source code meets quality standards