[6.0.x] Fixed #36264 -- Excluded proxy neighbors of parents from deletion collection when keep_parents=True.

Signed-off-by: saJaeHyukc <wogur981208@gmail.com>

Backport of 748551fea0 from main.

tests/delete/models.py

@@ -32,6 +32,11 @@ class RChild(R):
     pass
 
 
+class RProxy(R):
+    class Meta:
+        proxy = True
+
+
 class RChildChild(RChild):
     pass
 
@@ -179,7 +184,7 @@ class RelToBase(models.Model):
 
 
 class Origin(models.Model):
-    pass
+    r_proxy = models.ForeignKey("RProxy", models.CASCADE, null=True)
 
 
 class Referrer(models.Model):