Fix crash when an attribute node was used inside an unary op (#8209)

Closes #8207

doc/whatsnew/fragments/8207.bugfix

@@ -0,0 +1,3 @@
+Fix a crash happening when a class attribute was negated in the start argument of an enumerate.
+
+Closes #8207

pylint/checkers/refactoring/refactoring_checker.py

@@ -2338,13 +2338,16 @@ def _enumerate_with_start(
         return False, confidence
 
     def _get_start_value(self, node: nodes.NodeNG) -> tuple[int | None, Confidence]:
-        if isinstance(node, (nodes.Name, nodes.Call, nodes.Attribute)):
+        if (
+            isinstance(node, (nodes.Name, nodes.Call, nodes.Attribute))
+            or isinstance(node, nodes.UnaryOp)
+            and isinstance(node.operand, nodes.Attribute)
+        ):
             inferred = utils.safe_infer(node)
             start_val = inferred.value if inferred else None
             return start_val, INFERENCE
         if isinstance(node, nodes.UnaryOp):
             return node.operand.value, HIGH
         if isinstance(node, nodes.Const):
             return node.value, HIGH
-
         return None, HIGH

tests/functional/r/regression_02/regression_8207.py

@@ -0,0 +1,14 @@
+"""Regression test for 8207."""
+
+# pylint: disable=missing-docstring,too-few-public-methods
+
+class Example:
+    def __init__(self):
+        self.offset = -10
+
+    def minus_offset(self):
+        return {
+            (x, x): value
+            for x, row in enumerate([(5, 10), (20, 30)])
+            for y, value in enumerate(row, -self.offset)
+        }