Update dependabot.yml for latest release of action

Author: gsidhwani-nr

.github/workflows/dependabot.yml

@@ -18,7 +18,7 @@ jobs:
       run: | 
           ./newrelic-dependencies.sh   
     - name: Setup Gradle to generate and submit dependency graphs
-      uses: gradle/gradle-build-action@dependency-graph
+      uses: gradle/gradle-build-action@v2.6.1
       with:
         dependency-graph: generate-and-submit
     - name: Run a build, generating the dependency graph snapshot which will be submitted