If the user modifies a WooCommerce block template but the theme doesn't include it, it will fail to save.

To reproduce

1. Amend WooCommerce Core or checkout this PR Update has_block_template function to use apply_filters woocommerce#30997
2. Add the following snippet in the directory specified:

/woo-blocks/templates/block-templates/single-product.html

<!-- wp:template-part {"slug":"header","tagName":"header","className":"site-header","layout":{"inherit":true} /-->
<!-- wp:paragraph --> <p>You are using the Woo Blocks block template now</p> <!-- /wp:paragraph -->
<!-- wp:template-part {"slug":"footer","tagName":"footer","className":"site-footer","layout":{"inherit":true} /-->

3. Go to Site Editor > Templates and modify the Single product template.
4. Try to save the template. If you take a look at the Network tab of your devtools, you will notice the request returned error 404. If you reload the page, you will notice the changes weren't saved.