x/vuln/cmd/govulncheck: unmask module versions in SBOM testdata

[zpavlinovic]

Go will soon release a feature where versions of the main module and dependencies built from an untagged or dirty commit produce a valid Go version. Before, those versions were (devel). The new change is already at go tip, making some of the tests fail that expect (devel) version. We currently mask the dirty versions with (devel) too, but when all builders' go versions have this feature, we should just use the actual version.