Add 'ms-vscode.extension-test-runner' to recommanded extensions

Needed to run tests from VS Code Testing view.

(no-issue-check)

Author: AnthonyLeonardoGracio

.vscode/extensions.json

@@ -7,6 +7,7 @@
       "davidanson.vscode-markdownlint",
       "esbenp.prettier-vscode",
       "dbaeumer.vscode-eslint",
-      "adacore.ada"
+      "adacore.ada",
+      "ms-vscode.extension-test-runner"
    ]
-}
+}