Fix Windows unit test invocation command (#321)

Fixes:

```
Error: @workflow/core#test: command (D:\a\workflow\workflow\packages\core) C:\Users\runneradmin\setup-pnpm\node_modules\.bin\.tools\pnpm\10.20.0\bin\pnpm.CMD run test exited (1)
> @workflow/[email protected] test D:\a\workflow\workflow\packages\core
> WORKFLOW_TARGET_WORLD=embedded vitest run src

'WORKFLOW_TARGET_WORLD' is not recognized as an internal or external command,
operable program or batch file.
 ELIFECYCLE  Test failed. See above for more details.
```

Author: TooTallNate

.changeset/cyan-bars-speak.md

@@ -0,0 +1,2 @@
+---
+---

packages/core/package.json

@@ -41,7 +41,7 @@
     "build": "tsc",
     "dev": "tsc --watch",
     "clean": "tsc --build --clean && rm -r dist ||:",
-    "test": "WORKFLOW_TARGET_WORLD=embedded vitest run src",
+    "test": "cross-env WORKFLOW_TARGET_WORLD=embedded vitest run src",
     "test:e2e": "vitest run e2e",
     "typecheck": "tsc --noEmit"
   },
@@ -69,7 +69,8 @@
     "@types/debug": "4.1.12",
     "@types/node": "catalog:",
     "@types/seedrandom": "3.0.8",
-    "@workflow/tsconfig": "workspace:*"
+    "@workflow/tsconfig": "workspace:*",
+    "cross-env": "10.1.0"
   },
   "peerDependencies": {
     "@opentelemetry/api": "1"