[FIX] Fix bad session labels in T1Linear pipeline (#1000)

* fix session labels in T1Linear

* Update clinica/pipelines/t1_linear/anat_linear_utils.py

Co-authored-by: Ghislain Vaillant <ghisvail@users.noreply.github.com>

---------

Co-authored-by: Ghislain Vaillant <ghisvail@users.noreply.github.com>

clinica/pipelines/t1_linear/anat_linear_utils.py

@@ -32,7 +32,13 @@ def _get_substitutions_datasink(bids_image_id: str, suffix: str) -> list:
     substitutions : List of tuples of str
         List of length 3 containing the substitutions to perform.
     """
-    bids_image_id_without_suffix = bids_image_id.rstrip(f"_{suffix}")
+    # TODO: Use str.removesuffix once Python 3.8 compatibility is dropped.
+    if bids_image_id.endswith(f"_{suffix}"):
+        bids_image_id_without_suffix = bids_image_id[: -(len(suffix) + 1)]
+    else:
+        raise ValueError(
+            f"bids image ID {bids_image_id} should end with provided {suffix}."
+        )
     return [
         (
             f"{bids_image_id}Warped_cropped.nii.gz",