fix(ci): use Kotlin DSL syntax instead of Groovy in build.gradle.kts

android/app/build.gradle.kts

@@ -4,10 +4,11 @@ plugins {
     id("dev.flutter.flutter-gradle-plugin")
 }
 
-def keystoreProperties = new Properties()
-def keystorePropertiesFile = rootProject.file("key.properties")
-if (keystorePropertiesFile.exists()) {
-    keystoreProperties.load(new FileInputStream(keystorePropertiesFile))
+val keystorePropertiesFile = rootProject.file("key.properties")
+val keystoreProperties = java.util.Properties().apply {
+    if (keystorePropertiesFile.exists()) {
+        load(keystorePropertiesFile.inputStream())
+    }
 }
 
 android {
@@ -33,25 +34,27 @@ android {
     }
 
     signingConfigs {
-        release {
+        create("release") {
             if (keystorePropertiesFile.exists()) {
-                keyAlias = keystoreProperties["keyAlias"]
-                keyPassword = keystoreProperties["keyPassword"]
-                storeFile = keystoreProperties["storeFile"] != null ? file(keystoreProperties["storeFile"]) : null
-                storePassword = keystoreProperties["storePassword"]
+                keyAlias = keystoreProperties["keyAlias"] as String?
+                keyPassword = keystoreProperties["keyPassword"] as String?
+                storeFile = keystoreProperties["storeFile"]?.let { file(it) }
+                storePassword = keystoreProperties["storePassword"] as String?
             }
         }
     }
 
     buildTypes {
         release {
-            signingConfig = keystorePropertiesFile.exists()
-                ? signingConfigs.release
-                : signingConfigs.debug
+            signingConfig = if (keystorePropertiesFile.exists()) {
+                signingConfigs.getByName("release")
+            } else {
+                signingConfigs.getByName("debug")
+            }
         }
     }
 }
 
 flutter {
     source = "../.."
-}
+}