Fix the too strict checking of batch evaluator literals for multistart.

[janosg]

Closes #604

[codecov]

Codecov Report

Attention: Patch coverage is 84.00000% with 4 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
src/optimagic/batch_evaluators.py	60.00%	2 Missing ⚠️
src/optimagic/deprecations.py	33.33%	2 Missing ⚠️

Files with missing lines	Coverage Δ
src/optimagic/differentiation/derivatives.py	96.18% <100.00%> (ø)
src/optimagic/differentiation/numdiff_options.py	98.48% <100.00%> (+0.09%)	⬆️
src/optimagic/optimization/multistart_options.py	95.67% <100.00%> (+0.05%)	⬆️
src/optimagic/optimizers/scipy_optimizers.py	96.80% <100.00%> (ø)
src/optimagic/typing.py	86.66% <100.00%> (ø)
src/optimagic/batch_evaluators.py	73.33% <60.00%> (-0.20%)	⬇️
src/optimagic/deprecations.py	99.07% <33.33%> (-0.93%)	⬇️

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