👌🚇 Improve result comparison threshold for spectra

[jsnel]

Issue identified in #936, comment reproduced below.

After the update we find that the result comparison still fails but only for a singular data point in one of the examples (log below). Digging a little deeper (looking at the plot) we find that the point of failure is at a place were the spectral value in question is very small (~-1.497), compared to the overall maximum of the spectrum (~7500). However, the spectra are compared locally (per wavelength) and the absolute tolerance for the comparison between results is scaled with the local value of the data, meaning that the tolerance for a point close to zero is much tighter than the tolerance for a point near the maximum. This is a point where the result comparison could be further refined, but for now we accept this as a PASS ✔️ and this PR may be merged.

FAILED .github/test_result_consistency.py::test_result_data_var_consistency[study_fluorescence-decay_associated_spectra]

E       AssertionError: Result data_var data mismatch: 'decay_associated_spectra' in 'dataset1.nc'.
E         With sum of absolute difference: 0.0039020775839004873 and shape: (49, 5)
E         Mean difference: 1.592684728122648e-05
E         
E       assert False
E        +  where False = <function allclose.<locals>._allclose at 0x7f40599e5790>(<xarray.DataArray 'decay_associated_spectra' (spectral: 49, component: 5)>\narray([[-145.581345,   52.590453,   21.6330...7\n    rate      (component) float64 ...\n    lifetime  (component) float64 ...\nDimensions without coordinates: component, <xarray.DataArray 'decay_associated_spectra' (spectral: 49, component: 5)>\narray([[-145.581346,   52.590453,   21.6330...7\n    rate      (component) float64 ...\n    lifetime  (component) float64 ...\nDimensions without coordinates: component, atol=array([[1.73546487e-05, 6.26927054e-06, 2.57886253e-06, 2.17881660e-06,\n        6.32769907e-06],\n       [1.50005268e-0...     5.91504505e-06],\n       [5.92400043e-05, 4.45607905e-05, 4.22466039e-06, 1.01596965e-04,\n        6.42848991e-06]]), rtol=1e-05, print_fail=20)

.github/test_result_consistency.py:221: AssertionError
----------------------------- Captured stdout call -----------------------------
allclose first 1 failures:
  (40, 1): -1.4969902223364386 -1.4969635695838823
=========================== short test summary info ============================
FAILED .github/test_result_consistency.py::test_result_data_var_consistency[study_fluorescence-decay_associated_spectra]

Originally posted by @jsnel in #935 (comment)