SymPy v2 cannot be loaded in CI with Julia v1.6

**Describe the bug**
I observe the following error in CI:

```
ERROR: LoadError: InitError: ArgumentError: ref of NULL PyObject
Stacktrace:
[1] _getproperty(o::PyCall.PyObject, s::Symbol)
@ PyCall ~/.julia/packages/PyCall/KLzIO/src/PyCall.jl:299
[2] __getproperty
@ ~/.julia/packages/PyCall/KLzIO/src/PyCall.jl:312 [inlined]
[3] getproperty(o::PyCall.PyObject, s::Symbol)
@ PyCall ~/.julia/packages/PyCall/KLzIO/src/PyCall.jl:318
[4] __init__()
@ SymPy ~/.julia/packages/SymPyCore/EgrjB/src/SymPy/sympy.jl:123
[5] _include_from_serialized(path::String, depmods::Vector{Any})
@ Base ./loading.jl:696
[6] _require_search_from_serialized(pkg::Base.PkgId, sourcepath::String)
@ Base ./loading.jl:782
[7] _require(pkg::Base.PkgId)
@ Base ./loading.jl:1020
[8] require(uuidkey::Base.PkgId)
@ Base ./loading.jl:936
[9] require(into::Module, mod::Symbol)
@ Base ./loading.jl:923
[10] include(fname::String)
@ Base.MainInclude ./client.jl:444
[11] top-level scope
@ none:6
during initialization of module SymPy
```

See https://github.com/ranocha/BSeries.jl/actions/runs/6978438964/job/18989851345?pr=180#step:7:213

**To Reproduce**
Run CI with SymPy.jl v2

**Expected behavior**
It can be loaded and doesn't throw an error.