PYTHONOPTIMIZE=1 causes KeyErrors
### Description

When I set the flag: `export PYTHONOPTIMIZE=1`, the code:
```
import jax.numpy as jnp
m = jnp.eye(5)
a = jnp.ones(5)
jnp.linalg.solve(m,a)
```
returns the following error:
```
The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "error.py", line 6, in <module>
    jnp.linalg.solve(m,a)
  File "/home/ben/.../python3.8/site-packages/jax/_src/numpy/linalg.py", line 553, in solve
    return lax_linalg._solve(a, b)
KeyError: 139645559661888
```

### What jax/jaxlib version are you using?

jax v0.3.21, jaxlib v0.3.20

### Which accelerator(s) are you using?

CPU

### Additional system info

Ubuntu, jax is installed into a site_packages repo for ROS.

### NVIDIA GPU info

_No response_
diff --git a/jax/interpreters/partial_eval.py b/jax/interpreters/partial_eval.py
index bfacfe16b..78e71da9b 100644
--- a/jax/interpreters/partial_eval.py
+++ b/jax/interpreters/partial_eval.py
@@ -898,7 +898,8 @@ def tracers_to_jaxpr(
 
   def newvar(t: JaxprTracer) -> Var:
     var = gensym(type_substitute(t.aval))
-    assert t_to_var.setdefault(id(t), var) is var
+    var_ = t_to_var.setdefault(id(t), var)
+    assert var is var_
     return var
 
   def type_substitute(aval: AbstractValue) -> AbstractValue:
['jax/interpreters/partial_eval.py']