test_all: run the Internet Archive tests with -short to speed them up

Every write operation waits for the server's processing tasks which
currently take minutes each, so the full test suite takes much longer
than the timeout. Running with -short skips the FsEncoding subtests
(which are already on the ignore list) and the chunked upload tests,
removing a large number of these waits.

fstest/test_all/config.yaml

@@ -213,6 +213,7 @@ backends:
  - backend:  "internetarchive"
    remote:   "TestIA:rclone-integration-test-2"
    fastlist: true
+   short:    true
    tests:
      - backend
    ignore: