editorconfig: don't trim trailing whitespace in tests

Author: lolbinarycat

.editorconfig

@@ -7,9 +7,12 @@ root = true
 [*]
 end_of_line = lf
 charset = utf-8
-trim_trailing_whitespace = true
 insert_final_newline = true
 
+# some tests need trailing whitespace in output snapshots
+[!tests/]
+trim_trailing_whitespace = true
+
 [!src/llvm-project]
 indent_style = space
 indent_size = 4