Bump io.undertow:undertow-core from 2.3.20.Final to 2.3.21.Final in /web/undertow/simple#107

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dependabot/maven/web/undertow/simple/io.undertow-undertow-core-2.3.21.Finaljanbodnar/Java-Advanced:dependabot/maven/web/undertow/simple/io.undertow-undertow-core-2.3.21.FinalCopy head branch name to clipboard