Fix ESLint tests

The upgrade to ESLint 7.0.0 broke our custom rule tests. It seems
we were affected by eslint/eslint#13293
after all.

R=jacktfranklin@chromium.org

Change-Id: I3dcf8b7e15f1bc6a26c2fa069f24241e87f07627
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2538840
Commit-Queue: Tim van der Lippe <tvanderlippe@chromium.org>
Commit-Queue: Jack Franklin <jacktfranklin@chromium.org>
Auto-Submit: Tim van der Lippe <tvanderlippe@chromium.org>
Reviewed-by: Jack Franklin <jacktfranklin@chromium.org>

scripts/eslint_rules/lib/check_license_header.js

@@ -187,7 +187,7 @@ module.exports = {
           return;
         }
 
-        const {leading: comments} = context.getComments(node.body[0]);
+        const comments = context.getSourceCode().getCommentsBefore(node.body[0]);
 
         if (!comments || comments.length === 0) {
           context.report({