Remove JL_GC_POP without corresponding push (#32075)
I'm fairly sure this fixes #32059, though I didn't rr that all the way to the end, but instead
used the static analyzer once I saw that it was a GC frame mismatch. The analyzer reports:
```
/home/keno/julia-old/src/jltypes.c:1603:5: warning: JL_GC_POP without corresponding push
JL_GC_POP();
^~~~~~~~~~~
```
Fix that.
