Poor failure message when go.sum contains a merge-conflict

[stefanpenner]

What version of gazelle are you using?

latest

What version of rules_go are you using?

latest

What version of Bazel are you using?

latest

Does this issue reproduce with the latest releases of all the above?

yes

What operating system and processor architecture are you using?

N/A

What did you do?

go.sum contains a merge-conflict

What did you expect to see?

An actionable error message

What did you see instead?

ERROR: Traceback (most recent call last):
	File "/private/var/tmp/_bazel_spenner/45bdcefdebc3485be9a2f641a09b7a9f/external/gazelle~override/internal/bzlmod/go_deps.bzl", line 473, column 55, in _go_deps_impl
		for entry, new_sum in sums_from_go_mod(module_ctx, from_file_tag.go_mod).items():
	File "/private/var/tmp/_bazel_spenner/45bdcefdebc3485be9a2f641a09b7a9f/external/gazelle~override/internal/bzlmod/go_mod.bzl", line 335, column 25, in sums_from_go_mod
		return parse_sumfile(module_ctx, go_mod_label, "go.sum")
	File "/private/var/tmp/_bazel_spenner/45bdcefdebc3485be9a2f641a09b7a9f/external/gazelle~override/internal/bzlmod/go_mod.bzl", line 365, column 24, in parse_sumfile
		return parse_go_sum(sum_content)
	File "/private/var/tmp/_bazel_spenner/45bdcefdebc3485be9a2f641a09b7a9f/external/gazelle~override/internal/bzlmod/go_mod.bzl", line 370, column 28, in parse_go_sum
		path, version, sum = line.split(" ")
Error: too few values to unpack (got 1, want 3)

[stefanpenner]

posting so I don't forget, I may try to tackle this if time permits.

[fmeum]

We should recommend the merge=union .gitattributes trick in docs.