A user has created a module called "my_test_module" and committed it to GitHub. Over time, several commits have been made with updates to the module, each tagged in GitHub with an incremental version

The @tag= syntax is not valid for Terraform Git module sources and is not recognized by Terraform's module loader.

The &ref= syntax is invalid because & is used to chain additional query parameters but the reference must start with ?ref= as the first query string parameter.

The #tag= syntax is invalid for Terraform Git sources because # denotes a URL fragment in HTTP, not a query parameter, and Terraform does not use it for version selection.

The correct syntax for referencing a specific Git tag in a Terraform module source is the ?ref= query parameter appended to the repository URL. The value git::https://example.com/my_test_module.git?ref=v1.0.4 instructs Terraform to check out the commit associated with the v1.0.4 tag when downloading the module.