[cronet] Use the same host and Android emulator architecture.

[brianquinlan]

macos-latest now refers to ARM machines, so use ubuntu-latest to be able to continue to use x86_64 Android images.

Why not just use ARM images? Because they are not supported below Android API v30.

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[github-actions]

Package publishing

Package	Version	Status	Publish tag (post-merge)
package:http_profile	0.1.0	ready to publish	http_profile-v0.1.0
package:cronet_http	1.2.0	already published at pub.dev
package:cupertino_http	1.4.1-wip	WIP (no publish necessary)
package:http	1.2.2-wip	WIP (no publish necessary)
package:web_socket	0.1.3	already published at pub.dev

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