Gradle: Declare dependencies correctly for local build

[skalarproduktraum]

This PR fixes an issue in the Gradle build file where sciview's dependencies were not declared correctly, leading to build failures when building against a local scenery version.

[kephale]

Codacy complaint was:

build.gradle.kts
Medium icon Medium Error Prone
Multiple occurrences of the same string literal within a single file detected. Prefer extracting the string literal into a property or constant.

val ktVersion = "1.8.20"

These are duplicated in multiple scopes, but the duplication is OK for me in these cases.