Fix syntax warning

Author: Taarini Sarath Chander

ncdiff/docs/changelog/undistributed/changelog_fix_syntax_warning_20241202082730.rst

@@ -0,0 +1,5 @@
+--------------------------------------------------------------------------------
+                                Fix
+--------------------------------------------------------------------------------
+* yang.ncdiff
+    * Fix syntax warning

ncdiff/src/yang/ncdiff/ref.py

@@ -362,7 +362,7 @@ def parse_square_bracket(self, to_node=None):
                             self.cut(start_idx+1, end_idx-2, tag, 2)
                         start_idx = None
                     else:
-                        if re.search('^\[[1-9][0-9]*\]$', substring):
+                        if re.search(r'^\[[1-9][0-9]*\]$', substring):
                             numbers = substring[1:-1]
                             self.cut(start_idx+1, end_idx-1, numbers, 2)
                         else: