test/system: Silence warning with Bats >= 1.7.0

Bats 1.7.0 emits a warning if a command passed to 'run' returns with an
exit code of 127 [1].

This requires Bats >= 1.5.0, which is present in Fedora >=35, and
supports specifying the exit code as an argument to Bats' 'run'
command [2].

However, bats_require_minimum_version can't be used, because it's
only available from Bats 1.7.0, which is new enough that it's absent in
Fedora 35.

[1] Bats commit c6dc2f88361a4f5b
    bats-core/bats-core#547
    https://bats-core.readthedocs.io/en/stable/warnings/BW01.html

[2] bats-core/bats-core#367
    bats-core/bats-core#507
    https://bats-core.readthedocs.io/en/stable/writing-tests.html

[3] Bats commit 71d6b71cebc3d32b
    bats-core/bats-core#556
    https://bats-core.readthedocs.io/en/stable/warnings/BW02.html

containers#1081

test/system/104-run.bats

@@ -145,7 +145,7 @@ teardown() {
 
   create_default_container
 
-  run $TOOLBOX run $cmd
+  run -127 $TOOLBOX run $cmd
 
   assert_failure
   assert [ $status -eq 127 ]