chore(python): skip docfx in main presubmit

.kokoro/build.sh

@@ -15,7 +15,11 @@
 
 set -eo pipefail
 
-cd github/google-auth-library-python
+if [[ -z "${PROJECT_ROOT:-}" ]]; then
+    PROJECT_ROOT="github/google-auth-library-python"
+fi
+
+cd "${PROJECT_ROOT}"
 
 # Disable buffering, so that the logs stream through.
 export PYTHONUNBUFFERED=1
@@ -30,16 +34,16 @@ export GOOGLE_APPLICATION_CREDENTIALS=${KOKORO_GFILE_DIR}/service-account.json
 export PROJECT_ID=$(cat "${KOKORO_GFILE_DIR}/project-id.json")
 
 # Remove old nox
-python3.6 -m pip uninstall --yes --quiet nox-automation
+python3 -m pip uninstall --yes --quiet nox-automation
 
 # Install nox
-python3.6 -m pip install --upgrade --quiet nox
-python3.6 -m nox --version
+python3 -m pip install --upgrade --quiet nox
+python3 -m nox --version
 
 # If NOX_SESSION is set, it only runs the specified session,
 # otherwise run all the sessions.
 if [[ -n "${NOX_SESSION:-}" ]]; then
-    python3.6 -m nox -s "${NOX_SESSION:-}"
+    python3 -m nox -s ${NOX_SESSION:-}
 else
-    python3.6 -m nox
+    python3 -m nox
 fi

.kokoro/docs/docs-presubmit.cfg

@@ -15,3 +15,14 @@ env_vars: {
     key: "TRAMPOLINE_IMAGE_UPLOAD"
     value: "false"
 }
+
+env_vars: {
+    key: "TRAMPOLINE_BUILD_FILE"
+    value: github/google-auth-library-python/.kokoro/build.sh"
+}
+
+# Only run this nox session.
+env_vars: {
+    key: "NOX_SESSION"
+    value: "docs docfx"
+}

synth.metadata

@@ -4,14 +4,14 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/google-auth-library-python.git",
-        "sha": "9c4200dff31986b7ff300126e9aa35d14aa84dba"
+        "sha": "647290a2dfc797067f7966c1dae512359e6bb7e7"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "da5c6050d13b4950c82666a81d8acd25157664ae"
+        "sha": "fb53b6fb373b7c3edf4e55f3e8036bc6d73fa483"
       }
     }
   ],