ci: update all n1-standard-4 type runners to n2-standard-4 (#8340)

Author: pkoutsovasilis

.buildkite/bk.integration.pipeline.yml

@@ -394,7 +394,7 @@ steps:
             limit: 1
         agents:
           provider: "gcp"
-          machineType: "n1-standard-4"
+          machineType: "n2-standard-4"
           image: "${IMAGE_UBUNTU_2404_X86_64}"
           diskSizeGb: 80
         matrix: