Changes & context

chore(gomod): Specs for go.mod directives unrelated to dependencies

This adds a few unit tests for go.mod directives that are not related to
dependencies: godebug, retract and single-line exclude. All of
those should be ignored.

The exclude directive prevents a module version from being loaded by
the go command.
https://go.dev/ref/mod#go-mod-file-exclude

Apparently they can be used to e.g. block a specific version of a
dependency which has a known vulnerability. Simply updating the
exclude section doesn't make the most sense as someone wanted to
exclude a specific version of a dependency.

Note: This commit doesn't fix the behaviour for multi-line excludes, it
just increases test coverage to show that single-line excludes are
already ignored.

References:

• https://go.dev/doc/modules/gomod-ref

fix(gomod): Exclude multi-line exclude directives from extraction

With #28852, suddenly
multiline exclude directives have been renovated.

Given that single-line exclude directives are not renovated, this just
aligns the behaviour between the two. In a future iteration the
excludes could be parsed in order to change the behaviour for renovate
with regards to the dependency updates, but it is unclear what that
would entail.

So simply skipping them could be good enough.

Side-note: The regex based parsing seems to be really tricky for a lock
file which might contain multi line blocks. One should consider
rewriting it in a proper loop.

References:

• go.mod exclude directive is ignored #31905

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