Add Wall of Browser Bugs entry for #20759

Refs https://bugs.webkit.org/show_bug.cgi?id=162362
Closes #20759
[ci skip]

docs/_data/browser-bugs.yml

@@ -460,6 +460,16 @@
   origin: >
     Bootstrap#12832
 
+-
+  browser: >
+    Safari (iOS)
+  summary: >
+    Element which is `position:fixed` disappears after opening a `<select>` menu
+  upstream_bug: >
+    WebKit#162362
+  origin: >
+    Bootstrap#20759
+
 -
   browser: >
     Safari (iPad Pro)