fix: pybamm.have_julia is True when PyCall.jl uninstalled

[awadell1]

Currently pybamm.have_julia() returns True even if PyCall.jl is not configured this results in test failures as the tests assume they can call:

from julia.api import Julia
Julia()

Which fails if Julia has not been configured. This commit fixes that.

Type of change

Please add a line in the relevant section of CHANGELOG.md to document the change (include PR #) - note reverse order of PR #s. If necessary, also add to the list of breaking changes.

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist:

• [] No style issues: $ flake8
• All tests pass: $ python run-tests.py --unit
• The documentation builds: $ cd docs and then $ make clean; make html

You can run all three at once, using $ python run-tests.py --quick.

Further checks:

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[valentinsulzer]

Thanks, will probably need to update this soon / coordinate with @abillscmu as we switch to pythoncall

[aabills]

I'll add a test but this should be obsolete when #2363 is merged.

[codecov]

Codecov Report

Base: 99.66% // Head: 99.72% // Increases project coverage by +0.05% 🎉

Coverage data is based on head (5f50b93) compared to base (c9e2aca).
Patch coverage: 100.00% of modified lines in pull request are covered.

❗ Current head 5f50b93 differs from pull request most recent head d421be3. Consider uploading reports for the commit d421be3 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #2402      +/-   ##
===========================================
+ Coverage    99.66%   99.72%   +0.05%     
===========================================
  Files          269      268       -1     
  Lines        20190    20153      -37     
===========================================
- Hits         20123    20097      -26     
+ Misses          67       56      -11     

Impacted Files	Coverage Δ
pybamm/util.py	100.00% <100.00%> (ø)
pybamm/citations.py	100.00% <0.00%> (ø)
pybamm/parameters/parameter_sets.py	100.00% <0.00%> (ø)
pybamm/parameters/parameter_values.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lithium_ion/Ai2020.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lithium_ion/Xu2019.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lead_acid/Sulzer2019.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lithium_ion/Chen2020.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lithium_ion/Ecker2015.py	100.00% <0.00%> (ø)
pybamm/input/parameters/lithium_ion/OKane2022.py	100.00% <0.00%> (ø)
... and 7 more

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