test: move trim to global helpers

test/helpers.lua

@@ -731,6 +731,10 @@ local function read_nvim_log()
   return log
 end
 
+local function trim(s)
+  return s:match('^%s*(.*%S)') or ''
+end
+
 local module = {
   REMOVE_THIS = REMOVE_THIS,
   argss_to_cmd = argss_to_cmd,
@@ -772,6 +776,7 @@ local module = {
   updated = updated,
   which = which,
   write_file = write_file,
+  trim = trim,
 }
 
 return module