uri_signing: fix warning which affects ubuntu:20.04 builds (#7717)
uri_signing: fix warning which affects ubuntu:20.04 builds (#7717)


pbchou/trafficserver,bryancall/trafficserver,duke8253/trafficserver,bryancall/trafficserver,duke8253/trafficserver,pbchou/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,bryancall/trafficserver,bryancall/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,duke8253/trafficserver,duke8253/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,pbchou/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver,vmamidi/trafficserver