Fix: ZBL test path (#3757)

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-->
## Summary by CodeRabbit


- **Tests**
- Updated the path configuration for the `use_srtab` key in test
settings to enhance reliability by changing from a relative path to an
absolute path.
- Imported `os` module and defined `CUR_DIR` as the directory of the
current file.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

source/tests/pt/model/test_permutation.py

@@ -1,5 +1,6 @@
 # SPDX-License-Identifier: LGPL-3.0-or-later
 import copy
+import os
 import unittest
 
 import torch
@@ -14,6 +15,8 @@
     env,
 )
 
+CUR_DIR = os.path.dirname(__file__)
+
 dtype = torch.float64
 
 model_se_e2_a = {
@@ -60,7 +63,7 @@
 
 model_zbl = {
     "type_map": ["O", "H", "B"],
-    "use_srtab": "source/tests/pt/model/water/data/zbl_tab_potential/H2O_tab_potential.txt",
+    "use_srtab": f"{CUR_DIR}/water/data/zbl_tab_potential/H2O_tab_potential.txt",
     "smin_alpha": 0.1,
     "sw_rmin": 0.2,
     "sw_rmax": 1.0,