fix(shorebird_cli): --split-per-abi incorrectly always enabled (#1042)

packages/shorebird_cli/lib/src/shorebird_build_mixin.dart

@@ -138,7 +138,7 @@ mixin ShorebirdBuildMixin on ShorebirdCommand {
   Future<void> buildApk({
     String? flavor,
     String? target,
-    bool? splitPerAbi,
+    bool splitPerAbi = false,
   }) async {
     const executable = 'flutter';
     final arguments = [
@@ -147,7 +147,7 @@ mixin ShorebirdBuildMixin on ShorebirdCommand {
       '--release',
       if (flavor != null) '--flavor=$flavor',
       if (target != null) '--target=$target',
-      if (splitPerAbi != null) '--split-per-abi',
+      if (splitPerAbi) '--split-per-abi',
       ...results.rest,
     ];
 

packages/shorebird_cli/test/src/commands/release/release_android_command_test.dart

@@ -375,6 +375,14 @@ void main() {
           status: ReleaseStatus.active,
         ),
       ).called(1);
+      const buildApkArguments = ['build', 'apk', '--release'];
+      verify(
+        () => shorebirdProcess.run(
+          'flutter',
+          buildApkArguments,
+          runInShell: true,
+        ),
+      ).called(1);
       expect(exitCode, ExitCode.success.code);
     });
 
@@ -401,7 +409,7 @@ void main() {
           status: ReleaseStatus.active,
         ),
       ).called(1);
-      final buildApkArguments = [
+      const buildApkArguments = [
         'build',
         'apk',
         '--release',