chore(flink): fix regex digit escape

This might not be sufficient for all regexes, but now sqlgot now stores
unescaped strings and then escapes them during generation, which for the
`Flink(Hive)` case meant doubling up backslashes on `\\d`

ibis/backends/sql/dialects.py

@@ -182,6 +182,8 @@ def new_name(names: set[str], name: str) -> str:
 
 
 class Flink(Hive):
+    UNESCAPED_SEQUENCES = {"\\\\d": "\\d"}
+
     class Generator(Hive.Generator):
         UNNEST_WITH_ORDINALITY = False