Move reckon configuration to settings.gradle.kts

[nulls]

What's done:

• moved configuration related to reckon to settings.gradle.kts as it's suggested in reckon's README.md

Should fix issues like here:

FAILURE: Build failed with an exception.

* Where:
Build file '/Users/runner/work/okio-extras/okio-extras/build.gradle.kts' line: 12

* What went wrong:
null cannot be cast to non-null type org.ajoberstar.grgit.Grgit

[github-actions]

JUnit Tests (EnricoMi/publish-unit-test-result-action, Java 11)

28 tests  ±0   28 ✅ ±0   0s ⏱️ ±0s
 2 suites ±0    0 💤 ±0 
 2 files   ±0    0 ❌ ±0 

Results for commit e79b148. ± Comparison against base commit d01e0fc.

[github-actions]

JUnit Tests (EnricoMi/publish-unit-test-result-action, Java 17)

28 tests  ±0   28 ✅ ±0   0s ⏱️ ±0s
 2 suites ±0    0 💤 ±0 
 2 files   ±0    0 ❌ ±0 

Results for commit e79b148. ± Comparison against base commit d01e0fc.