bpo-35283: Add deprecation warning for Thread.isAlive (GH-11454)

Add a deprecated warning for the threading.Thread.isAlive() method.
diff --git a/Lib/threading.py b/Lib/threading.py
index bb41456..7bc8a85 100644
--- a/Lib/threading.py
+++ b/Lib/threading.py
@@ -1091,7 +1091,15 @@
         self._wait_for_tstate_lock(False)
         return not self._is_stopped
 
-    isAlive = is_alive
+    def isAlive(self):
+        """Return whether the thread is alive.
+
+        This method is deprecated, use is_alive() instead.
+        """
+        import warnings
+        warnings.warn('isAlive() is deprecated, use is_alive() instead',
+                      DeprecationWarning, stacklevel=2)
+        return self.is_alive()
 
     @property
     def daemon(self):