build: move system and samples test from Node 10 to Node 12 (#94)

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Source-Link: googleapis/synthtool@05de3e1

Author: yoshi-automation

packages/google-cloud-billing/synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/nodejs-billing.git",
-        "sha": "355931be004e7f11c4132d3696d7d826aab105be"
+        "sha": "7be157c25bfadcd0576c947242fed2a341b92a56"
       }
     },
     {
@@ -19,7 +19,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "1a60ff2a3975c2f5054431588bd95db9c3b862ba"
+        "sha": "05de3e1e14a0b07eab8b474e669164dbd31f81fb"
       }
     }
   ],
@@ -51,19 +51,19 @@
     ".kokoro/common.cfg",
     ".kokoro/continuous/node10/common.cfg",
     ".kokoro/continuous/node10/docs.cfg",
-    ".kokoro/continuous/node10/lint.cfg",
-    ".kokoro/continuous/node10/samples-test.cfg",
-    ".kokoro/continuous/node10/system-test.cfg",
     ".kokoro/continuous/node10/test.cfg",
     ".kokoro/continuous/node12/common.cfg",
+    ".kokoro/continuous/node12/lint.cfg",
+    ".kokoro/continuous/node12/samples-test.cfg",
+    ".kokoro/continuous/node12/system-test.cfg",
     ".kokoro/continuous/node12/test.cfg",
     ".kokoro/docs.sh",
     ".kokoro/lint.sh",
     ".kokoro/populate-secrets.sh",
     ".kokoro/presubmit/node10/common.cfg",
-    ".kokoro/presubmit/node10/samples-test.cfg",
-    ".kokoro/presubmit/node10/system-test.cfg",
     ".kokoro/presubmit/node12/common.cfg",
+    ".kokoro/presubmit/node12/samples-test.cfg",
+    ".kokoro/presubmit/node12/system-test.cfg",
     ".kokoro/presubmit/node12/test.cfg",
     ".kokoro/publish.sh",
     ".kokoro/release/docs-devsite.cfg",
@@ -86,15 +86,13 @@
     "README.md",
     "api-extractor.json",
     "linkinator.config.json",
-    "package-lock.json.1098049865",
     "protos/google/cloud/billing/v1/cloud_billing.proto",
     "protos/google/cloud/billing/v1/cloud_catalog.proto",
     "protos/protos.d.ts",
     "protos/protos.js",
     "protos/protos.json",
     "renovate.json",
     "samples/README.md",
-    "samples/package-lock.json.2846676223",
     "src/index.ts",
     "src/v1/cloud_billing_client.ts",
     "src/v1/cloud_billing_client_config.json",