Pushforward fails for the cuspidal cubic immersion

Nobody has claimed this yet.

I don't understand what is going wrong here:
```m2
needsPackage "NormalToricVarieties"

P1 = toricProjectiveSpace 1
P2 = toricProjectiveSpace 2
f = inducedMap map(P2, P1, matrix{{-2},{1}})
S = ring P1

pushForward_f S^{2}
```
This gives the error:
```m2
stdio:6:12:(3): error: not implemented yet: unexpected degree map of ring map
```
Which comes from here:
https://github.com/Macaulay2/M2/blob/ec65028f1527076b663279b1311188caa9e22b67/M2/Macaulay2/m2/pushforward.m2#L147-L151
What is this check for?

Note that the map is sending the variables of P^2 to `{x_0*x_1^2, x_0^3, x_1^3}`, all degree 3, and both source and target are standard graded.

@mikestillman @ggsmith any ideas?

Reproduce the example in the issue, then inspect the degree-map check in M2/Macaulay2/m2/pushforward.m2 at lines 147-151. Determine why this map reaches the unexpected-degree error despite the stated grading, and define done as making the pushforward computation handle this example without that error.

Written by the indexing model from the issue text.