Add Edge entry for #20507 to Wall of Browser Bugs

Closes #20507

[skip sauce]

Author: cvrebert

docs/_data/browser-bugs.yml

@@ -88,6 +88,16 @@
   origin: >
     Bootstrap#19670
 
+-
+  browser: >
+    Microsoft Edge
+  summary: >
+    Active `position: fixed;` `<button>` flickers when scrolling
+  upstream_bug: >
+    Edge#8770398
+  origin: >
+    Bootstrap#20507
+
 -
   browser: >
     Firefox