fix: include platform in user agent #3951

Job	Run time
Build	2m 47s
Test example js-libp2p-example-browser-pubsub	3m 8s
Test example js-libp2p-example-chat	1m 14s
Test example js-libp2p-example-circuit-relay	1m 4s
Test example js-libp2p-example-connection-encryption	1m 33s
Test example js-libp2p-example-custom-protocols	1m 0s
Test example js-libp2p-example-delegated-routing	2m 19s
Test example js-libp2p-example-discovery-mechanisms	1m 34s
Test example js-libp2p-example-peer-and-content-routing	1m 46s
Test example js-libp2p-example-pnet	1m 4s
Test example js-libp2p-example-protocol-and-stream-muxing	1m 9s
Test example js-libp2p-example-pubsub	1m 9s
Test example js-libp2p-example-transports	1m 7s
Test example js-libp2p-example-webrtc-private-to-private	1m 56s
	22m 50s

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