Add targeted rule-disabling

This turns off one rule for the job definition test, as the
CodeMirror component is failing:
https://dequeuniversity.com/rules/axe/3.5/scrollable-region-focusable

ui/tests/acceptance/job-definition-test.js

@@ -21,7 +21,7 @@ module('Acceptance | job definition', function(hooks) {
   });
 
   test('it passes an accessibility audit', async function(assert) {
-    await a11yAudit();
+    await a11yAudit('scrollable-region-focusable');
     assert.ok(true, 'a11y audit passes');
   });
 

ui/tests/helpers/a11y-audit.js

@@ -1,17 +1,16 @@
 import a11yAudit from 'ember-a11y-testing/test-support/audit';
 
-export default async function defaultA11yAudit() {
-  await a11yAudit({
-    rules: {
-      'color-contrast': {
-        enabled: false
-      },
-      'heading-order': {
-        enabled: false
-      },
-      'scrollable-region-focusable': {
-        enabled: false
-      },
+export default async function defaultA11yAudit(...overriddenRules) {
+  const rules = {
+    'color-contrast': {
+      enabled: false
+    },
+    'heading-order': {
+      enabled: false
     }
-  });
+  };
+
+  overriddenRules.forEach(rule => rules[rule] = { enabled: false });
+
+  await a11yAudit({rules});
 }