Use logger in dependency graph init script (#191)

Dependency graph init script now uses Gradle logger to emit warning/info messages.
This allows these messages to be suppressed using `--quiet`.

sources/src/resources/init-scripts/gradle-actions.github-dependency-graph.init.gradle

@@ -12,7 +12,7 @@ if (gradleVersion < GradleVersion.version("5.2") ||
   if (getVariable('GITHUB_DEPENDENCY_GRAPH_CONTINUE_ON_FAILURE') != "true") {
     throw new GradleException("Dependency Graph is not supported for ${gradleVersion}. No dependency snapshot will be generated.")
   }
-  println "::warning::Dependency Graph is not supported for ${gradleVersion}. No dependency snapshot will be generated."
+  logger.warn("::warning::Dependency Graph is not supported for ${gradleVersion}. No dependency snapshot will be generated.")
   return
 }
 
@@ -23,11 +23,11 @@ if (isTopLevelBuild) {
   def reportFile = getUniqueReportFile(getVariable('GITHUB_DEPENDENCY_GRAPH_JOB_CORRELATOR'))
 
   if (reportFile == null) {
-    println "::warning::No dependency snapshot generated for step. Could not determine unique job correlator - specify GITHUB_DEPENDENCY_GRAPH_JOB_CORRELATOR var for this step."
+    logger.warn("::warning::No dependency snapshot generated for step. Could not determine unique job correlator - specify GITHUB_DEPENDENCY_GRAPH_JOB_CORRELATOR var for this step.")
     return
   }
 
-  println "Generating dependency graph into '${reportFile}'"
+  logger.lifecycle("Generating dependency graph into '${reportFile}'")
 }
 
 apply from: 'gradle-actions.github-dependency-graph-gradle-plugin-apply.groovy'