Disable auto-injected codesign validation task on CI (#4387)

Sets flag in CI YML that will turn off the auto-injected codesign validation
task since CI is a non-production pipeline.

build/pipelines/ci.yml

@@ -19,6 +19,10 @@ pr:
       - samples/*
       - tools/*
 
+variables:
+  - name: runCodesignValidationInjectionBG
+    value: false
+
 #     0.0.yyMM.dd##
 #     0.0.1904.0900
 name: 0.0.$(Date:yyMM).$(Date:dd)$(Rev:rr)