ftp: fix flaky UploadTimeout test on slow integration servers

The test set the short idle timeout before creating the test Fs, which
made fs.NewFs fail to read the FTP welcome banner within 1s on slow CI
hosts. Restore the long timeout while NewFs dials the control
connection, then apply the short idle timeout before the upload so the
data connection still exercises the close race that shut_timeout fixes.

backend/ftp/ftp_internal_test.go

@@ -52,13 +52,21 @@ func (f *Fs) testUploadTimeout(t *testing.T) {
 		ci.Timeout = saveTimeout
 	}()
 	ci.LowLevelRetries = 1
-	ci.Timeout = fs.Duration(idleTimeout)
 
 	upload := func(concurrency int, shutTimeout time.Duration) (obj fs.Object, err error) {
+		// Use the saved (long) timeout while NewFs dials the FTP control
+		// connection and reads the welcome banner. On slow CI servers this
+		// can take longer than idleTimeout, which would cause a spurious
+		// i/o timeout before the test can run. The connection's idle
+		// deadline is captured at dial time, so the data connection
+		// dialled later inside Put will still get idleTimeout - which is
+		// what the test is actually trying to exercise.
+		ci.Timeout = saveTimeout
 		fixFs := deriveFs(ctx, t, f, settings{
 			"concurrency":  concurrency,
 			"shut_timeout": shutTimeout,
 		})
+		ci.Timeout = fs.Duration(idleTimeout)
 
 		// Make test object
 		fileTime := fstest.Time("2020-03-08T09:30:00.000000000Z")