chore(python): skip docfx in main presubmit (#1166)

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Synth log will be available here:
https://source.cloud.google.com/results/invocations/0b6bbaa2-1b46-45ec-a4bd-ef2b18c764b2/targets

- [ ] To automatically regenerate this PR, check this box.

Source-Link: googleapis/synthtool@fb53b6f

Author: yoshi-automation

.kokoro/build.sh

@@ -15,7 +15,11 @@
 
 set -eo pipefail
 
-cd github/google-api-python-client
+if [[ -z "${PROJECT_ROOT:-}" ]]; then
+    PROJECT_ROOT="github/google-api-python-client"
+fi
+
+cd "${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

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/google-api-python-client.git",
-        "sha": "32d1c597b364e2641eca33ccf6df802bb218eea1"
+        "sha": "cc94ec86e652769e9d3d5cb6d6491efb8d76dd21"
       }
     },
     {
@@ -18,7 +18,7 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "c2de32114ec484aa708d32012d1fa8d75232daf5"
+        "sha": "fb53b6fb373b7c3edf4e55f3e8036bc6d73fa483"
       }
     }
   ],