Ensure to close connection to VM after collecting coverage (#50943)

packages/flutter_tools/lib/src/test/coverage_collector.dart

diff --git a/packages/flutter_tools/lib/src/test/coverage_collector.dart b/packages/flutter_tools/lib/src/test/coverage_collector.dart
index e89dc42..72171bc 100644
--- a/packages/flutter_tools/lib/src/test/coverage_collector.dart
+++ b/packages/flutter_tools/lib/src/test/coverage_collector.dart
@@ -181,7 +181,10 @@
 }) async {
   final VMService vmService = await connector(serviceUri);
   await vmService.getVM();
-  return _getAllCoverage(vmService, libraryPredicate);
+  final Map<String, dynamic> result = await _getAllCoverage(
+      vmService, libraryPredicate);
+  await vmService.close();
+  return result;
 }
 
 Future<Map<String, dynamic>> _getAllCoverage(VMService service, bool Function(String) libraryPredicate) async {

packages/flutter_tools/lib/src/vmservice.dart

diff --git a/packages/flutter_tools/lib/src/vmservice.dart b/packages/flutter_tools/lib/src/vmservice.dart
index 7fc4664..f18f802 100644
--- a/packages/flutter_tools/lib/src/vmservice.dart
+++ b/packages/flutter_tools/lib/src/vmservice.dart
@@ -452,6 +452,8 @@
   Future<void> getVM() async => await vm.reload();
 
   Future<void> refreshViews({ bool waitForViews = false }) => vm.refreshViews(waitForViews: waitForViews);
+
+  Future<void> close() async => await _peer.close();
 }
 
 /// An error that is thrown when constructing/updating a service object.