Bump spek_version from 2.0.14 to 2.0.15 in /samples/jvm/spek

Bumps `spek_version` from 2.0.14 to 2.0.15.

Updates `spek-dsl-jvm` from 2.0.14 to 2.0.15
- [Release notes](https://github.com/spekframework/spek/releases)
- [Changelog](https://github.com/spekframework/spek/blob/2.x/docs/breaking-changes.md)
- [Commits](spekframework/spek@2.0.14...2.0.15)

Updates `spek-runner-junit5` from 2.0.14 to 2.0.15
- [Release notes](https://github.com/spekframework/spek/releases)
- [Changelog](https://github.com/spekframework/spek/blob/2.x/docs/breaking-changes.md)
- [Commits](spekframework/spek@2.0.14...2.0.15)

Signed-off-by: dependabot[bot] <support@github.com>

samples/jvm/spek/build.gradle

@@ -6,7 +6,7 @@ import org.gradle.api.tasks.testing.logging.TestExceptionFormat
 buildscript {
     ext {
         atrium_version = '0.14.0'
-        spek_version = '2.0.14'
+        spek_version = '2.0.15'
     }
 }