Remove Kotest "extension()" and "install()" work-arounds

[sschuberth]

That's what I had tried, but then I ran into some issue with a db lateinit property not being initialized.

Did you check in which situations, especially if the third example I gave in kotest/kotest#3555 still fails?

It doesn't happen during test runtime, but during test initialization. Do I do not even come as far as being able to tell whether the test fails or succeeds.

I can have a look after the merge.

Originally posted by @mnonnenmacher in #3369 (comment)

[sschuberth]

As a reminder, this is about

ort-server/shared/ktor-utils/src/testFixtures/kotlin/AbstractAuthorizationTest.kt

Lines 88 to 91 in 62ef05f

	// The "extension()" and "install()" functions cannot be used above because of
	// https://github.com/kotest/kotest/issues/3555.
	// TODO: Check if this is fixed once Kotest 6 is released.
	override val extensions: List<Extension> = listOf(dbExtension, keycloakExtension)