FIX: Remove unexpected n_jobs kwarg in PET estimator instantiation

Remove unexpected `n_jobs` kwarg in PET estimator instantiation.

Fixes:
```
Cell In[17], line 6
      3 estimator = PETMotionEstimator()
      5 # Run the estimator
----> 6 affines = estimator.run(
      7     pet_dataset,
      8     omp_nthreads=4,
      9     n_jobs=4,
     10 )

TypeError: PETMotionEstimator.run() got an unexpected keyword argument 'n_jobs'
```

Author: jhlegarreta

docs/notebooks/pet_motion_estimation.ipynb

@@ -2263,7 +2263,6 @@
     "affines = estimator.run(\n",
     "    pet_dataset,\n",
     "    omp_nthreads=4,\n",
-    "    n_jobs=4,\n",
     ")"
    ]
   },