[Gradle, Wasm] Use static source sets accessors for wasm

^KT-62955 fixed

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/resources/testProject/new-mpp-wasm-wasi-js-test/app/build.gradle.kts

@@ -15,13 +15,13 @@ kotlin {
     }
 
     sourceSets {
-        val wasmJsMain by getting {
+        wasmJsMain {
             dependencies {
                 implementation(project(":lib"))
             }
         }
 
-        val wasmWasiMain by getting {
+        wasmWasiMain {
             dependencies {
                 implementation(project(":lib"))
             }