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

@@ -112,6 +112,8 @@ def _interval_with_precision(self, e):
 
 
 class Flink(Hive):
+    UNESCAPED_SEQUENCES = {"\\\\d": "\\d"}
+
     class Generator(Hive.Generator):
         TYPE_MAPPING = Hive.Generator.TYPE_MAPPING.copy() | {
             sge.DataType.Type.TIME: "TIME",