vscode: replace deprecated setting

This change was made automatically by VS Code since `true` has been
deprecated.

Author: dlech

.vscode/settings.json

@@ -3,7 +3,7 @@
         "editor.defaultFormatter": "ms-python.black-formatter",
         "editor.formatOnSave": true,
         "editor.codeActionsOnSave": {
-            "source.organizeImports": true
+            "source.organizeImports": "explicit"
         },
       },
       "black-formatter.importStrategy": "fromEnvironment",