ErrorSubscriber: also marks the error causes as reported

Fix: rails#53938

In some cases like `Template::Error`, the error may be unwrapped
up the stack and end up being reported twice.

Author: byroot

activesupport/lib/active_support/error_reporter.rb

@@ -232,8 +232,11 @@ def report(error, handled: true, severity: handled ? :warning : :error, context:
         end
       end
 
-      unless error.frozen?
-        error.instance_variable_set(:@__rails_error_reported, true)
+      while error
+        unless error.frozen?
+          error.instance_variable_set(:@__rails_error_reported, true)
+        end
+        error = error.cause
       end
 
       nil

activesupport/test/error_reporter_test.rb

@@ -269,6 +269,31 @@ class ErrorReporterTest < ActiveSupport::TestCase
     end
   end
 
+  test "causes can't be reported again either" do
+    begin
+      begin
+        begin
+          raise "Original"
+        rescue
+          raise "Another"
+        end
+      rescue
+        raise "Yet Another"
+      end
+    rescue => @error
+    end
+
+    assert_difference -> { @subscriber.events.size }, +1 do
+      @reporter.report(@error, handled: false)
+    end
+
+    assert_no_difference -> { @subscriber.events.size } do
+      3.times do
+        @reporter.report(@error.cause.cause, handled: false)
+      end
+    end
+  end
+
   test "can report frozen exceptions" do
     assert_difference -> { @subscriber.events.size }, +1 do
       @reporter.report(@error.freeze, handled: false)