Bump octicons from 19.14.0 to 19.15.0 in /demo (#3325)

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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
       racc (~> 1.4)
     nokogiri (1.18.1-x86_64-linux-gnu)
       racc (~> 1.4)
-    octicons (19.14.0)
+    octicons (19.15.0)
     oj (3.16.3)
       bigdecimal (>= 3.0)
     os (1.1.4)