Only override the current project buffer-locally

* lisp/progmodes/project.el (project-switch-project): Only
override the current project buffer-locally.  This is mostly for
the the mode-line indicator (https://debbugs.gnu.org/66317#53).

lisp/progmodes/project.el

@@ -2030,8 +2030,11 @@ to directory DIR."
   (let ((command (if (symbolp project-switch-commands)
                      project-switch-commands
                    (project--switch-project-command))))
-    (let ((project-current-directory-override dir))
-      (call-interactively command))))
+    (unwind-protect
+        (progn
+          (setq-local project-current-directory-override dir)
+          (call-interactively command))
+      (kill-local-variable 'project-current-directory-override))))
 
 ;;;###autoload
 (defun project-uniquify-dirname-transform (dirname)