call out the behavior when PAC file download fails (#22464)

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https://docker.slack.com/archives/C02DDPKLJ0J/p1744707532756369?thread_ts=1744293644.289759&cid=C02DDPKLJ0J

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Author: karman-docker

content/manuals/security/for-admins/hardened-desktop/air-gapped-containers.md

@@ -52,6 +52,7 @@ The `containersProxy` setting describes the policy which is applied to traffic f
 > [!IMPORTANT]
 >
 > Any existing `proxy` setting in the `admin-settings.json` file continues to apply to traffic from the app on the host.
+> If the PAC file download fails, the Docker Desktop app and its containers do not block the request; instead, they attempt to connect directly to the target URL.
 
 ## Example PAC file