[bugfix] Fix the incorrect with-statement

[aaa123git]

You may want to enter multiple context managers in one with-statement.
However, with rng_context and fp8_context is equivalent to with fp8_context, because rng_context doesn't rewrite __and__ method.
The correct way is with rng_context, fp8_context: .

Ref: https://docs.python.org/3/reference/compound_stmts.html#the-with-statement