So... I tested this deployment in 3 different ways and what I found was that:
Directly cloning the repo with
cdto the static folder, and deploying from there, reproduced the issue, but only if I did it from my Google Cloud Shell.
a. I later found out that the Go version I had in the Cloud Shell was the Go 1.12.
b. I created a new VM instance to test it from a fresh Go 1.11 environment and the same process worked like a treat.
The same process as the above, but instead of deploying from the static, I moved its content to a different directory and then I deployed it from there.
a. This worked in the VM instance and in the Cloud Shell.
As suggested in the Quickstart for Go 1.11 in the App Engine Standard Environment, I downloaded the sample code using the
cdto the static folder and deployed from there.
a. This also worked in both environments.
My suggestion is to always try to download Google's golang samples using the
go get command, as it is suggested in the guides and it did not mess with the App Engine deployment in the tests I made.
It is also important to mention that both environments had the same Cloud SDK version, which is the 259.