BLT not ignoring local Behat config file

[geerlingguy]

After updating to BLT 8.6.4, I noticed the following when comparing changed files:

On branch master
Your branch is up-to-date with 'origin/master'.
Changes not staged for commit:
  (use "git add <file>..." to update what will be committed)
  (use "git checkout -- <file>..." to discard changes in working directory)

	modified:   .gitignore
	modified:   blt/.schema_version
	modified:   blt/project.yml
	modified:   composer.json
	modified:   composer.lock

Untracked files:
  (use "git add <file>..." to include in what will be committed)

	tests/behat/local.yml

no changes added to commit (use "git add" and/or "git commit -a")

Note the addition of tests/behat/local.yml. I think I missed this file when I was testing the local.* gitignore change for #797