Tests

fix: `files_upload_v2` usage in README #1418

Job	Run time
test (ruby=2.7)	21s
test (ruby=2.7, concurrency=async-websocket)	22s
test (ruby=3.0)	18s
test (ruby=3.1)	21s
test (ruby=3.2)	20s
test (ruby=3.3)	22s
test (ruby=3.4)	20s
test (ruby=ruby-head)	26s
test (ruby=jruby-head)	20s
coveralls	0s
	3m 10s

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