fix: include platform in user agent #3948

Job	Run time
Build	3m 3s
Test example js-libp2p-example-browser-pubsub	1m 50s
Test example js-libp2p-example-chat	1m 3s
Test example js-libp2p-example-circuit-relay	2m 26s
Test example js-libp2p-example-connection-encryption	1m 27s
Test example js-libp2p-example-custom-protocols	1m 49s
Test example js-libp2p-example-delegated-routing	2m 35s
Test example js-libp2p-example-discovery-mechanisms	1m 19s
Test example js-libp2p-example-peer-and-content-routing	1m 32s
Test example js-libp2p-example-pnet	2m 48s
Test example js-libp2p-example-protocol-and-stream-muxing	1m 36s
Test example js-libp2p-example-pubsub	1m 14s
Test example js-libp2p-example-transports	1m 23s
Test example js-libp2p-example-webrtc-private-to-private	2m 18s
	26m 23s

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