fix(engine/postgresql): Correct aggregate func sig (#1182)

Author: kyleconroy

internal/endtoend/testdata/func_aggregate/go/db.go

@@ -0,0 +1,10 @@
+-- Example queries for sqlc
+CREATE TABLE authors (
+  id   BIGSERIAL PRIMARY KEY,
+  name text      NOT NULL,
+  bio  text
+);
+
+-- name: Percentile :one
+select percentile_disc(0.5) within group (order by authors.name)
+from authors;

internal/endtoend/testdata/func_aggregate/go/models.go

@@ -0,0 +1,11 @@
+{
+  "version": "1",
+  "packages": [
+    {
+      "path": "go",
+      "name": "querytest",
+      "schema": "query.sql",
+      "queries": "query.sql"
+    }
+  ]
+}