Tests

Added `files_upload_external` (#533) #1368

Job	Run time
test (ruby=2.7)	52s
test (ruby=2.7, concurrency=async-websocket)	51s
test (ruby=3.0)	32s
test (ruby=3.1)	31s
test (ruby=3.2)	30s
test (ruby=3.3)	34s
test (ruby=ruby-head)	32s
test (ruby=jruby-head)	2m 8s
coveralls	4s
	6m 34s

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