MSC4140: delayed event content as text, not bytes (#19360)

Store the JSON content of scheduled delayed events as text instead of a
byte array. This brings it in line with the `event_json` table's `json`
column, and fixes the inability to schedule a delayed event with
non-ASCII characters in its content.

Fixes #19242

scripts-dev/check_schema_delta.py

@@ -187,6 +187,14 @@ def check_schema_delta(delta_files: list[str], force_colors: bool) -> bool:
         sql_lang = "postgres"
         if delta_file.endswith(".sqlite"):
             sql_lang = "sqlite"
+        elif delta_file.endswith(".py"):
+            click.secho(
+                f"Skipping Python delta file: '{delta_file}'",
+                fg="yellow",
+                bold=True,
+                color=force_colors,
+            )
+            return True
 
         statements = sqlglot.parse(delta_contents, read=sql_lang)