Chore: should ignore appcenter.key in foss build

app/build.gradle.kts

@@ -47,6 +47,7 @@ android {
             dimension = "premium"
             versionNameSuffix = ".premium"
 
+            if (buildFlavor == "premium") {
                 val appCenterKey = rootProject.file("local.properties").inputStream()
                     .use { Properties().apply { load(it) } }
                     .getProperty("appcenter.key", null)
@@ -56,6 +57,7 @@ android {
                 buildConfigField("String", "APP_CENTER_KEY", "\"$appCenterKey\"")
             }
         }
+    }
 
     val signingFile = rootProject.file("keystore.properties")
     if (signingFile.exists()) {