fix: revert workspaceSearchPaths default to empty array to prevent PET configure timeout

The default `["./**/.venv"]` introduced in microsoft#1191 causes the PET server
to recursively walk the entire workspace during `configure`, which
exceeds the 30s timeout (microsoft#1154) on large workspaces. PET's built-in Venv
locator already discovers .venv directories at workspace roots without
needing extra search paths.

Affected versions: v1.18.0, v1.18.1, v1.20.0, v1.20.1, v1.22.0, and main
(v1.16.0 and earlier used an empty default and are not affected).

Fixes environment discovery failure on workspaces with deep directory
trees (e.g. ML projects with datasets, checkpoints, vendored repos).

Author: Gorluxor

package.json

@@ -124,7 +124,7 @@
                 "python-envs.workspaceSearchPaths": {
                     "type": "array",
                     "description": "%python-envs.workspaceSearchPaths.description%",
-                    "default": ["./**/.venv"],
+                    "default": [],
                     "scope": "resource",
                     "items": {
                         "type": "string"