fix(lsp-mode): add "tmp" to ignored directory names

Rails projects uses a "tmp" directory for asset compilation, which can
lead to thousands of olders, which lsp-mode will try to monitor, and
warns that you're about to monitor +1000 directories.

Hence, ignore "tmp" directories, as there shouldn't be any code in there
that needs a language server.

modules/lsp/siren-lsp.el

@@ -63,6 +63,9 @@
       (lsp-format-buffer)))
 
   :config
+  ;; Add "tmp" directories to ignored list of directories.
+  (add-to-list 'lsp-file-watch-ignored-directories "[/\\\\]tmp")
+
   (define-minor-mode lsp-format-buffer-on-save-mode
     "Run lsp-format-buffer as a before-save-hook."
     :lighter " fmt"