Two polynomial SIGABRT bugs

[grhkm21]

Steps To Reproduce

sage: R = GF(2^8)["x"]
....: a = pow(R.random_element(8), 2, R.zero())
------------------------------------------------------------------------
(no backtrace available)
------------------------------------------------------------------------
Unhandled SIGABRT: An abort() occurred.
This probably occurred because a *compiled* module has a bug
in it and is not properly wrapped with sig_on(), sig_off().
Python will now terminate.
------------------------------------------------------------------------

sage: K.<x> = Zmod(4)[]
....: R.<z> = K.quotient_ring(x^2 - 1)
....: c = 2 * z + 1
....: f = 2 * z + 2
....: print("ok:", c * f)
....: f = f.lift().change_ring(Zmod(2))
....: print(" f:", f)
....: print("not ok:", c * f)
ok: 2*z + 2
 f: 0
Flint exception (Impossible inverse):
    Cannot invert modulo 2*0
------------------------------------------------------------------------
(no backtrace available)
------------------------------------------------------------------------
Unhandled SIGABRT: An abort() occurred.
This probably occurred because a *compiled* module has a bug
in it and is not properly wrapped with sig_on(), sig_off().
Python will now terminate.
------------------------------------------------------------------------

Expected Behavior

It should error out

Actual Behavior

crash

Additional Information

No response

Environment

- **OS**: Mac
- **Sage Version**: Since 2nd June 2023

Checklist

• I have searched the existing issues for a bug report that matches the one I want to file, without success.
• I have read the documentation and troubleshoot guide

[grhkm21]

I fixed the first bug already. For the second bug, I've been trying to trace the call stack for like an hour now but it's very difficult. I have reduced it to this:

sage: R = Zmod(4)["x"].quotient_ring(var("x")^2 - 1, names="z")
....: S = Zmod(2)["x"]
....: S(2 * R.0)