fix(neotest): support adapter key on adapter for playwright (#3824)

## What is this PR for?

Similar to https://github.com/LazyVim/LazyVim/issues/847 , only this
adapter adds a setup function into the 'adapter' key in the plugin table
([source](f61463f5c7/lua/neotest-playwright/init.lua (L31-L33))).

It is somewhat annoying that neotest does not provide a recommended way
for adapters to define their configuration function (at least not
explicitly)...

Perhaps we should work around it temporarily, but reach out to either
neotest or neotest-playwright authors?

## Does this PR fix an existing issue?

I didn't see anyone complaining about playwright adapter in issues or
discussions :/

## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/test/core.lua

@@ -86,6 +86,9 @@ return {
               local meta = getmetatable(adapter)
               if adapter.setup then
                 adapter.setup(config)
+              elseif adapter.adapter then
+                adapter.adapter(config)
+                adapter = adapter.adapter
               elseif meta and meta.__call then
                 adapter(config)
               else