Go: ignore vendor directory for multi-language repo

README.md

In a multi-language repository—for example, one that includes both Go and Ruby—you can run into conflicts around the vendor/ directory. Ruby commonly uses a vendor/ directory to store dependencies, but Go’s toolchain assumes that a vendor/ directory follows its own vendoring format (including the modules.txt file that defines vendored modules).

If Ruby’s vendor/ directory is present, the Go toolchain may attempt to interpret it as a Go vendoring directory, leading to unexpected errors.

To prevent this, configure Go to use module mode explicitly and ignore the vendor/ directory (which, in this case, is only relevant to Ruby):

• Add -mod=mod to commands such as go build and go test.
• Set a global flag with export GOFLAGS=-mod=mod for commands like go tool that do not expose a -mod flag directly.