fix: use test mode as not production

[rtritto]

Test mode should be used for test and development and not for production.

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[eandre]

What problem is this change solving for you? I'm not sure this is the right thing to do to in the general case.

[rtritto]

In development, usually the process.env.NODE_ENV is undefined or development. So when I started, I got:

file:///C:/Users/<USER>/AppData/Local/Yarn/Berry/cache/encore.dev-npm-1.44.6-3d86b75c4d-10c0.zip/node_modules/encore.dev/dist/internal/runtime/mod.js:5
export const RT = new Runtime({
                  ^

Error: failed to initialize runtime: unable to parse app metadata file

Caused by:
    failed to read file: The system cannot find the path specified. (os error 3)
    at file:///C:/test-encore-win/Local/Yarn/Berry/cache/encore.dev-npm-1.44.6-3d86b75c4d-10c0.zip/node_modules/encore.dev/dist/internal/runtime/mod.js:5:19
    at ModuleJob.run (node:internal/modules/esm/module_job:262:25)
    at async onImport.tracePromise.__proto__ (node:internal/modules/esm/loader:483:26)
    at async asyncRunEntryPointWithESMLoader (node:internal/modules/run_main:117:5) {
  code: 'GenericFailure'
}

because of: https://github.com/encoredev/encore/blob/af07a53709ed9942f7fc6a1489cec3ff539aaa54/runtimes/js/encore.dev/internal/runtime/mod.ts#L6