Add explicit junit launcher dependency

Author: JordonPhillips

codegen/buildSrc/src/main/kotlin/smithy-python.java-conventions.gradle.kts

@@ -37,6 +37,7 @@ dependencies {
     testImplementation(platform(libs.junit.bom))
     testImplementation(libs.junit.jupiter.api)
     testRuntimeOnly(libs.junit.jupiter.engine)
+    testRuntimeOnly("org.junit.platform:junit-platform-launcher")
     testImplementation(libs.junit.jupiter.params)
     compileOnly("com.github.spotbugs:spotbugs-annotations:${spotbugs.toolVersion.get()}")
     testCompileOnly("com.github.spotbugs:spotbugs-annotations:${spotbugs.toolVersion.get()}")