Allow for missing go directive in go.mod

[JamieMagee]

What are you trying to accomplish?

We're seeing the following issue in some repositories

Passed `nil` into T.must
file_parser.rb:70:in 'Dependabot::GoModules::FileParser#go_version

The issue is that the go directive in go.mod files was optional before Go 1.21¹. So some projects which rely on vendor dependencies that have not been updated since then will not have the go directive.

The go directive sets the minimum version of Go required to use this module. Before Go 1.21, the directive was advisory only; now it is a mandatory requirement: Go toolchains refuse to use modules declaring newer Go versions.

This change makes it optional in Dependabot as well.

Anything you want to highlight for special attention from reviewers?

How will you know you've accomplished your goal?

Checklist

• I have run the complete test suite to ensure all tests and linters pass.
• I have thoroughly tested my code changes to ensure they work as expected, including adding additional tests for new functionality.
• I have written clear and descriptive commit messages.
• I have provided a detailed description of the changes in the pull request, including the problem it addresses, how it fixes the problem, and any relevant details about the implementation.
• I have ensured that the code is well-documented and easy to understand.

Footnotes

1. https://go.dev/doc/modules/gomod-ref#go ↩