Bump octicons from 19.19.0 to 19.21.1 in /demo (#3797)

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

demo/Gemfile.lock

@@ -243,7 +243,7 @@ GEM
     nio4r (2.7.4)
     nokogiri (1.19.0-x86_64-linux-gnu)
       racc (~> 1.4)
-    octicons (19.19.0)
+    octicons (19.21.1)
     oj (3.16.10)
       bigdecimal (>= 3.0)
       ostruct (>= 0.2)