fix: bump smithy-kotlin version to enable protocol tests to work after Smithy 1.23 upgrade (#684)

Author: ianbotsf

gradle.properties

@@ -12,7 +12,7 @@ sdkVersion=0.17.5-SNAPSHOT
 smithyVersion=1.23.0
 smithyGradleVersion=0.6.0
 # smithy-kotlin codegen and runtime are versioned together
-smithyKotlinVersion=0.12.4
+smithyKotlinVersion=0.12.5-SNAPSHOT
 
 # kotlin
 kotlinVersion=1.7.10