feat(tasks): add shell task for check-python with venv activation (#25686)

fixes #24121

since extension developers are frequently changing their shell
activation settings, this provides a way to activate the venv then run
the task to allow for consistent checks by developers that mirror CI

Author: eleanorjboyd

.vscode/tasks.json

@@ -39,6 +39,24 @@
             "problemMatcher": ["$python"],
             "label": "npm: check-python",
             "detail": "npm run check-python:ruff && npm run check-python:pyright"
+        },
+        {
+            "label": "npm: check-python (venv)",
+            "type": "shell",
+            "command": "bash",
+            "args": ["-lc", "source .venv/bin/activate && npm run check-python"],
+            "problemMatcher": [],
+            "detail": "Activates the repo .venv first (avoids pyenv/shim Python) then runs: npm run check-python",
+            "windows": {
+                "command": "pwsh",
+                "args": [
+                    "-NoProfile",
+                    "-ExecutionPolicy",
+                    "Bypass",
+                    "-Command",
+                    ".\\.venv\\Scripts\\Activate.ps1; npm run check-python"
+                ]
+            }
         }
     ]
 }