fix quadratic backtracking in debug f-string quote detection (#5165)

CHANGES.md

diff --git a/CHANGES.md b/CHANGES.md
index a92a0ed..a68f06d 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -54,6 +54,8 @@
 <!-- Changes that improve Black's performance. -->
 
 - Improve performance on strings containing many consecutive backslashes (#5163)
+- Improve performance when merging implicitly concatenated f-strings whose expressions
+  contain long string literals (#5165)
 
 ### Output
 

src/black/trans.py

diff --git a/src/black/trans.py b/src/black/trans.py
index 8563089..26f9c96 100644
--- a/src/black/trans.py
+++ b/src/black/trans.py
@@ -641,7 +641,7 @@ def make_naked(string: str, string_prefix: str) -> str:
                     for span in iter_fexpr_spans(string)
                 ]
                 debug_expressions_contain_visible_quotes = any(
-                    re.search(r".*[\'\"].*(?<![!:=])={1}(?!=)(?![^\s:])", expression)
+                    re.search(r"[\'\"].*(?<![!:=])={1}(?!=)(?![^\s:])", expression)
                     for expression in f_expressions
                 )
                 if not debug_expressions_contain_visible_quotes: