fix: postCreate.sh doesn't execute without providing execute permissi…

…on to the script first (#33166)

Co-authored-by: hubwriter <hubwriter@github.com>

content/codespaces/developing-in-a-codespace/rebuilding-the-container-in-a-codespace.md

@@ -53,7 +53,7 @@ If you want to preserve files outside the `/workspaces` directory over a rebuild
 ```json
 {
     "image": "mcr.microsoft.com/devcontainers/base:alpine",
-    "postCreateCommand": ".devcontainer/postCreate.sh"
+    "postCreateCommand": "chmod +x .devcontainer/postCreate.sh && .devcontainer/postCreate.sh"
 }
 ```