Update atomicfu version to 0.26.1 (#4283)

Author: mvicsokolova

gradle.properties

@@ -4,7 +4,7 @@ group=org.jetbrains.kotlinx
 kotlin_version=2.0.0
 kotlin_language_version=2.0
 # DO NOT rename this property without adapting kotlinx.train build chain:
-atomicfu_version=0.25.0
+atomicfu_version=0.26.1
 
 # Dependencies
 junit_version=4.12