Pin runtime to python37 for dev_appserver
Pin runtime to python37 for dev_appserver

Otherwise, we get an exception that says "Unknown runtime 'python38'",
because dev_appserver doesn't see this as valid. Instead, we can just
pin it to something seen as "python3", even though it ends up using the
system python underneath

[nodeploy]

the-blue-alliance/the-blue-alliance,the-blue-alliance/the-blue-alliance,the-blue-alliance/the-blue-alliance,the-blue-alliance/the-blue-alliance,the-blue-alliance/the-blue-alliance,the-blue-alliance/the-blue-alliance