Avoid Groovy secret env var interpolation (#6505)

Jenkinsfile

@@ -243,7 +243,7 @@ pipeline {
                                     // Replace covermode values with set just for coveralls to reduce the variability in reports.
                                     sh 'awk \'NR==1{print "mode: set";next} $NF>0{$NF=1} {print}\' cover_ce.out > cover_ce_coveralls.out'
                                     sh 'which goveralls' // check if goveralls is installed
-                                    sh "goveralls -coverprofile=cover_ce_coveralls.out -service=uberjenkins -repotoken=${COVERALLS_TOKEN} || true"
+                                    sh 'goveralls -coverprofile=cover_ce_coveralls.out -service=uberjenkins -repotoken=$COVERALLS_TOKEN || true'
                                 }
                             }
                         }