Gerrit release: remove extra $ in the tag step

The conditional execution of the tag step was
referring to the param variable with a $ which is
incorrect as it isn't inside a string expansion
expression.

Change-Id: Ib584a9cdbb14ea7e29a83b993acc2dd8404e018d
diff --git a/jenkins-internal/gerrit-release.groovy b/jenkins-internal/gerrit-release.groovy
index 42d5f36..45746ee 100644
--- a/jenkins-internal/gerrit-release.groovy
+++ b/jenkins-internal/gerrit-release.groovy
@@ -54,7 +54,7 @@
 
         stage('Confirm and push tag') {
             when {
-                expression { $params.DRY_RUN == false }
+                expression { params.DRY_RUN == false }
             }
             steps {
                 dir('gerrit') {