build!: update library to use Node 12 (#835)

* build!: update library to use Node 12
* build: fix broken Kokoro configuration test
* build: import version from package.json for tests

Author: sofisl

.github/sync-repo-settings.yaml

@@ -34,7 +34,6 @@ branchProtectionRules:
     - "cla/google"
     - "docs"
     - "lint"
-    - "test (10)"
     - "test (12)"
     - "test (14)"
     - "test (16)"

.github/workflows/ci.yaml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node: [10, 12, 14, 16]
+        node: [12, 14, 16]
     steps:
       - uses: actions/checkout@v3
       - uses: actions/setup-node@v3