fix: correct ESCAPABLE_CHARS in query_lang tokenizer

Replace duplicate double-quote with single-quote so that
escaped single quotes inside single-quoted strings are
handled correctly (e.g. 'O''Brien' now tokenizes as O'Brien
instead of O'Brien).

Discovered during automated code review.

src/tagstudio/core/query_lang/tokenizer.py

@@ -61,7 +61,7 @@ class Tokenizer:
     pos: int
     current_char: str | None
 
-    ESCAPABLE_CHARS = ["\\", '"', '"']
+    ESCAPABLE_CHARS = ["\\", '"', "'"]
     NOT_IN_ULITERAL = [":", " ", "[", "]", "(", ")", "=", ","]
 
     def __init__(self, text: str) -> None: