test: close active editor to reduce number of open tabs

To reduce flakiness of the tests, we close the editor tab once the tests
for a specific file have been run. This seems to reduce the flakiness of
the tests and help slightly with the freezes on Windows.

Author: punchagan

src/test/suite/basic.test.ts

@@ -235,6 +235,9 @@ suite("Extension Features", function () {
         result.length,
         "No diagnostics after change",
       );
+      await vscode.commands.executeCommand(
+        "workbench.action.closeActiveEditor",
+      );
     }).timeout(SCAN_TIMEOUT);
   });
 });