num quantiles arg should use _parse_bitwise

Author: treysp

sqlglot/dialects/bigquery.py

@@ -924,7 +924,7 @@ def _parse_approx_quantiles(self) -> t.Optional[exp.Expression]:
                 this = self.expression(exp.Distinct, expressions=[this])
 
             self._match(TokenType.COMMA)
-            expression = self._parse_disjunction()
+            expression = self._parse_bitwise()
             if not expression:
                 self.raise_error("Expected number of quantiles argument in APPROX_QUANTILES")