Show error instead of warning when an incorrect tag entry is present

[Ellivers]

Currently, Spyglass shows a warning for nonexistent entries in tags, despite Minecraft showing an error for it and failing to load the tag.

This applies to all tags, not just function tags.

[misode]

I don't think we're going to change this. The undeclaredSymbol linting rule is a warning by default, mostly because it is not a syntax error and because there are some occations where this is not a problem (using a #c:something tag, referencing symbols from a dependency, other pack, or mod)

[Ellivers]

In this case, it's pretty much a syntax error. Would it be possible to handle tags differently compared to other places where undeclaredSymbol is used?

[misode]

@Ellivers I don't immediately see why tags should be handled differently. It is possible to manually configure this linting check to emit an error, see https://spyglassmc.com/user/lint/undeclaredSymbol