ci: use v1.5 fork of CI

Loads the exact CI when NRF:v1.5 was tagged

Signed-off-by: Thomas Stilwell <Thomas.Stilwell@nordicsemi.no>

Author: thst-nordic

Jenkinsfile

@@ -6,7 +6,7 @@
 // express written agreement with Nordic Semiconductor ASA.
 //
 
-@Library("CI_LIB") _
+@Library("CI_LIB@v1.5-branch") _
 
 def pipeline = new ncs.sdk_nrfxlib.Main()