Fix broken querySelectors on techdocs

This change fixes the broken pattern for selecting DOM elements to scroll to.

Previously it had error messages like so:
```
Uncaught DOMException: Failed to execute 'querySelector' on 'Element': '#fn:someidtag' is not a valid selector.
```

This did not bode well with the techdocs integration with footnotes.

The query has now changed to include something that is expected by the DOM queries.

Signed-off-by: Nicolas Arnold <nic@roadie.io>

.changeset/silver-panthers-occur.md

@@ -0,0 +1,5 @@
+---
+'@backstage/plugin-techdocs': patch
+---
+
+Fix broken query selectors on techdocs

plugins/techdocs/src/reader/components/Reader.tsx

@@ -803,7 +803,7 @@ export const useTechDocsReaderDom = (
                 navigate(`${parsedUrl.pathname}${parsedUrl.hash}`);
                 // Scroll to hash if it's on the current page
                 transformedElement
-                  ?.querySelector(`#${parsedUrl.hash.slice(1)}`)
+                  ?.querySelector(`[id='${parsedUrl.hash.slice(1)}']`)
                   ?.scrollIntoView();
               }
             } else {