Bump org.jetbrains.dokka from 1.8.10 to 1.8.20 #213

Unit Tests Report: Gradle 8.1.1 @ ubuntu-latest ✅

Report	Passed	Time
build/test-results/test/TEST-org.jetbrains.grammarkit.GrammarKitPluginSpec.xml	2✅	9s
build/test-results/test/TEST-org.jetbrains.grammarkit.tasks.GenerateLexerTaskSpec.xml	2✅	61s
build/test-results/test/TEST-org.jetbrains.grammarkit.tasks.GenerateParserTaskSpec.xml	2✅	2s

2 tests were completed in 9s with 2 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
org.jetbrains.grammarkit.GrammarKitPluginSpec	2✅			9s

✅ support centralized repository declaration
✅ grammarKit-specific tasks

2 tests were completed in 61s with 2 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
org.jetbrains.grammarkit.tasks.GenerateLexerTaskSpec	2✅			61s

✅ reuse configuration cache
✅ run lexer

2 tests were completed in 2s with 2 passed, 0 failed and 0 skipped.

Test suite	Passed	Failed	Skipped	Time
org.jetbrains.grammarkit.tasks.GenerateParserTaskSpec	2✅			2s

✅ run parser
✅ reuse configuration cache