Multiline comment at start of schema raises `SchemaParseError`

[ginger51011]

The following schema will raise a SchemaParseError if put at the top of a schema file

"""
This is a multiline comment
"""
schema {
    query: RootQuery
}

# ...

on the form

SchemaParseError(Syntax { message: " --> 1:1\n  |\n1 | \"\"\"\n  | ^---\n  |\n  = expected type_system_definition", start: Pos(1:1), end: None })

while the following is fine

# This comment is OK
schema {
    query: RootQuery
}

# ...