Improve `go.sum` parser

[ejortega]

Updates the go.sum parser to filter out modules with <version>/go.mod. These modules aren't not used to build the package but used to perform minimal version selection.

Part of https://github.com/phylum-dev/cli/issues/1396

Checklist

• [x] Does this PR have an associated issue (i.e., closes #<issueNum> in description above)?
• [x] Have you ensured that you have met the expected acceptance criteria?
• [x] Have you created sufficient tests?
• [x] Have you updated all affected documentation?
• [x] Have you updated CHANGELOG.md (or extensions/CHANGELOG.md), if applicable