fix: add button labels (#1031)

[![PR App][icn]][demo] | Fix RM-XYZ
:-------------------:|:----------:

## 🧰 Changes

adds button labels to Lightbox 

## 🧬 QA & Testing

- [Broken on production][prod].
- [Working in this PR app][demo].


[demo]: https://markdown-pr-PR_NUMBER.herokuapp.com
[prod]: https://SUBDOMAIN.readme.io
[icn]:
https://user-images.githubusercontent.com/886627/160426047-1bee9488-305a-4145-bb2b-09d8b757d38a.svg

__tests__/__snapshots__/index.test.js.snap

@@ -335,7 +335,7 @@ exports[`export multiple Markdown renderers > renders plain markdown as React 1`
 
 exports[`heading 1`] = `"<h2 class=\\"heading heading-2 header-scroll\\" align=\\"\\"><div class=\\"heading-anchor anchor waypoint\\" id=\\"example-header\\"></div><div class=\\"heading-text\\"><div id=\\"section-example-header\\" class=\\"heading-anchor_backwardsCompatibility\\"></div>Example Header</div><a aria-label=\\"Skip link to Example Header\\" class=\\"heading-anchor-icon fa fa-anchor\\" href=\\"#example-header\\"></a></h2>"`;
 
-exports[`image 1`] = `"<span aria-label="Image" class="img lightbox closed" role="button" tabindex="0"><span class="lightbox-inner"><img src="http://example.com/image.png" width="auto" height="auto" title="" class="img  " alt="Image" loading="lazy"></span></span>"`;
+exports[`image 1`] = `"<span aria-label="Expand image" class="img lightbox closed" role="button" tabindex="0"><span class="lightbox-inner"><img src="http://example.com/image.png" width="auto" height="auto" title="" class="img  " alt="Image" loading="lazy"></span></span>"`;
 
 exports[`list items 1`] = `
 "<ul>

__tests__/components/__snapshots__/index.test.ts.snap

@@ -10,4 +10,4 @@ exports[`Components > Embed 3`] = `"<div class="embed embed_hasImg"><a class="em
 
 exports[`Components > Embed 4`] = `"<div class="embed "><a class="embed-link" href="https://www.nytimes.com/2020/05/03/us/politics/george-w-bush-coronavirus-unity.html" rel="noopener noreferrer" target="_blank"><div class="embed-body"><small class="embed-provider">nytimes.com</small><div class="embed-title">rdmd</div></div></a></div>"`;
 
-exports[`Components > Image 1`] = `"<span aria-label="Bro eats pizza and makes an OK gesture." class="img lightbox closed" role="button" tabindex="0"><span class="lightbox-inner"><img src="https://files.readme.io/6f52e22-man-eating-pizza-and-making-an-ok-gesture.jpg" width="auto" height="auto" title="Pizza Face" class="img  " alt="Bro eats pizza and makes an OK gesture." loading="lazy"></span></span>"`;
+exports[`Components > Image 1`] = `"<span aria-label="Expand image" class="img lightbox closed" role="button" tabindex="0"><span class="lightbox-inner"><img src="https://files.readme.io/6f52e22-man-eating-pizza-and-making-an-ok-gesture.jpg" width="auto" height="auto" title="Pizza Face" class="img  " alt="Bro eats pizza and makes an OK gesture." loading="lazy"></span></span>"`;

components/Image/index.tsx

@@ -88,7 +88,7 @@ const Image = (Props: ImageProps) => {
 
   return (
     <span
-      aria-label={alt}
+      aria-label={`${lightbox ? 'Collapse image' : 'Expand image'}`}
       className={`img lightbox ${lightbox ? 'open' : 'closed'}`}
       onClick={toggle}
       onKeyDown={handleKeyDown}