Bump rack from 3.1.15 to 3.1.16 in /demo (#3516)

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

Author: dependabot[bot]

demo/Gemfile.lock

@@ -270,7 +270,7 @@ GEM
     puma (6.6.0)
       nio4r (~> 2.0)
     racc (1.8.1)
-    rack (3.1.15)
+    rack (3.1.16)
     rack-cors (3.0.0)
       logger
       rack (>= 3.0.14)