fix(test): add shellcheck disable for unused variables in fixtures

Author: Chemaclass

tests/acceptance/fixtures/strict_mode_setup_unset_variable.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# shellcheck disable=SC2034
 
 function set_up() {
         local result="prefix_${UNDEFINED_VAR}_suffix"

tests/acceptance/fixtures/test_bashunit_risky_no_assertions.sh

@@ -1,4 +1,5 @@
 #!/usr/bin/env bash
+# shellcheck disable=SC2034
 
 function test_has_no_assertions() {
         local user="invalid"