macros: Fix non-simple macro usage without message

[Turbo87]

Motivation

If something like warn!(?foo) and warn!(name: "foo", ?foo) works, then warn!(name: "foo", target: "foo_events", ?foo) should arguably also work. Before this change the more complicated variants of the macros however required a message argument, due to the usage of the + specifier in the macro definitions.

Solution

This commit changes the + (1 or more) to * (0 or more), which matches how the field tokens are used in the simpler variants of the macro.

~Note that this PR includes https://github.com/tokio-rs/tracing/pull/2878 to avoid merge conflicts, since they both target the same lines.~

[Turbo87]

lint failure should be fixed now, but looks like it needs a workflow approval again 😅

[Turbo87]

I've now rebased the branch to get rid of the merge conflict that was created by the squash merge of #2878 😅