GBLinear: Inplace predict is not supported by current booster.

GBLinear model is not thread-safe and cannot be easily deployed to production.

XGBRegressor(random_state=0, booster="gblinear")

```
Traceback (most recent call last):
File "/usr/local/lib/python3.11/site-packages/mlserver/parallel/worker.py", line 136, in _process_request
return_value = await method(
^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/mlserver_xgboost/xgboost.py", line 88, in predict
outputs = self._get_model_outputs(payload)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/mlserver_xgboost/xgboost.py", line 79, in _get_model_outputs
y = predict_fn(decoded_request)
^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/xgboost/sklearn.py", line 1114, in predict
predts = self.get_booster().inplace_predict(
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "/usr/local/lib/python3.11/site-packages/xgboost/core.py", line 2292, in inplace_predict
_check_call(
File "/usr/local/lib/python3.11/site-packages/xgboost/core.py", line 279, in _check_call
raise XGBoostError(py_str(_LIB.XGBGetLastError()))
xgboost.core.XGBoostError: [22:57:35] /workspace/include/xgboost/gbm.h:120: Inplace predict is not supported by current booster.
Stack trace:
[bt] (0) /usr/local/lib/python3.11/site-packages/xgboost/lib/libxgboost.so(+0x1f69e0) [0xffff736569e0]
[bt] (1) /usr/local/lib/python3.11/site-packages/xgboost/lib/libxgboost.so(+0x2148a0) [0xffff736748a0]
[bt] (2) /usr/local/lib/python3.11/site-packages/xgboost/lib/libxgboost.so(+0x65938) [0xffff734c5938]
[bt] (3) /usr/local/lib/python3.11/site-packages/xgboost/lib/libxgboost.so(XGBoosterPredictFromDense+0xd4) [0xffff734c5db4]
[bt] (4) /usr/lib/aarch64-linux-gnu/libffi.so.7(+0x6048) [0xffff84b1b048]
[bt] (5) /usr/lib/aarch64-linux-gnu/libffi.so.7(+0x5770) [0xffff84b1a770]
[bt] (6) /usr/local/lib/python3.11/lib-dynload/_ctypes.cpython-311-aarch64-linux-gnu.so(+0x1235c) [0xffff84b4035c]
[bt] (7) /usr/local/lib/python3.11/lib-dynload/_ctypes.cpython-311-aarch64-linux-gnu.so(+0x12a90) [0xffff84b40a90]
[bt] (8) /usr/local/bin/../lib/libpython3.11.so.1.0(_PyObject_MakeTpCall+0x2c8) [0xffff8abf7518]
```

Start with xgboost/sklearn.py at predict, xgboost/core.py at inplace_predict, and the GBLinear failure reported at include/xgboost/gbm.h:120. Reproduce the XGBRegressor booster="gblinear" case, then verify that prediction works for this booster and add or run coverage for the reported deployment scenario.

Written by the indexing model from the issue text.