Make eslint ignore js files in JH folder when in jh [RUN AS-IF-FOSS]

What does this MR do?

Make the eslint-as-if-foss ci job work when in jh, see details gitlab-jh/gitlab!67 (comment 651487680) @pslaughter could you help me review this MR? CC: @qianzhangxa

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Does this MR meet the acceptance criteria?

Conformity

• I have included changelog trailers, or none are needed. (Does this MR need a changelog?)
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• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.
• This change is backwards compatible across updates, or this does not apply.

Availability and Testing

• I have added/updated tests following the Testing Guide, or it's not needed. (Consider all test levels. See the Test Planning Process.)
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Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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