Fix server-side testing with vitest/ssr

[benoitv-code]

Fix server-side testing with vitest/ssr

Initial error

Initial error when running vitest in ssr mode, since [email protected] (introduced by #173, reported by #211):

Error: renderToString is not supported in the browser, returning undefined
    at throwInBrowser (.../node_modules/solid-js/web/dist/dev.js:1089:15)

Proposed fix

• This PR proposes not adding 'browser' if options.ssr is set

I am not familiar with the code, and I am not sure if it could lead to issues for other setups.
An alternative could be to only add 'browser' if the conditions don't already include 'node':

-...(isTestMode && !opts.isSsrTargetWebworker ? ['browser'] : []),
+...(isTestMode && !opts.isSsrTargetWebworker && !config.resolve.conditions.includes('node') ? ['browser'] : []),

Let me know which solution seems to be the best.

Additional note

The opts.isSsrTargetWebworker check seems to be inconsistant in the original code, I've left it untouched as I am not sure what is the intent there:

// Original code: Uses `client` conditions if isSsrTargetWebworker is set
if (config.consumer === 'client' || name === 'client' || opts.isSsrTargetWebworker) {

// Original  code: Later, not using `browser` condition if isSsrTargetWebworker set
...(isTestMode && !opts.isSsrTargetWebworker ? ['browser'] : []),

Can original author comment on if the original logic seems consistent? (cc @bluwy @brenelz)

Thanks!

---

Fixes #211