build(python): fail nox sessions if a python version is missing (#51)

Nox's default behavior is to quietly skip if a python interpreter is missing. https://nox.thea.codes/en/stable/usage.html#failing-sessions-when-the-interpreter-is-missing

Source-Author: Bu Sun Kim <8822365+busunkim96@users.noreply.github.com>
Source-Date: Tue Mar 16 13:38:02 2021 -0600
Source-Repo: googleapis/synthtool
Source-Sha: eda422b90c3dde4a872a13e6b78a8f802c40d0db
Source-Link: googleapis/synthtool@eda422b

noxfile.py

@@ -41,6 +41,9 @@
     "docs",
 ]
 
+# Error if a python version is missing
+nox.options.error_on_missing_interpreters = True
+
 
 @nox.session(python=DEFAULT_PYTHON_VERSION)
 def lint(session):

synth.metadata

@@ -4,7 +4,7 @@
       "git": {
         "name": ".",
         "remote": "https://github.com/googleapis/python-analytics-data.git",
-        "sha": "8fd57a340b7e052dc9c4d6c33882add75405eb8b"
+        "sha": "e7fa3bd5817a51e852b47c427f598ef02f935437"
       }
     },
     {
@@ -19,14 +19,14 @@
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2c54c473779ea731128cea61a3a6c975a08a5378"
+        "sha": "eda422b90c3dde4a872a13e6b78a8f802c40d0db"
       }
     },
     {
       "git": {
         "name": "synthtool",
         "remote": "https://github.com/googleapis/synthtool.git",
-        "sha": "2c54c473779ea731128cea61a3a6c975a08a5378"
+        "sha": "eda422b90c3dde4a872a13e6b78a8f802c40d0db"
       }
     }
   ],