Fixes problem with crop-tgrid

The function xr_crop_tgrid_data was failing tests. The issue has been identified and fixed. This implements the fix from !25.

pyicon/tests/test_docs.py

+import subprocess
+import pytest
+import pyicon as pyic
+from pathlib import Path
+
+
+def test_docs_build(tmpdir_factory):
+    base_dir = Path(pyic.__file__).parent / ".."
+    doc_dir = base_dir.resolve() / "doc"
+    build_dir = tmpdir_factory.mktemp("_build")
+
+    # Run the sphinx-build command
+    try:
+        subprocess.check_call(
+            ["sphinx-build", "-b", "html", doc_dir, build_dir])
+    except subprocess.CalledProcessError as e:
+        pytest.fail(
+            f"Documentation build failed with exit code {e.returncode}")