[Bug]: The union of errors can only be passed to ResourceCreate.

### Describe the bug

The union of errors can only be passed to ResourceCreate.

### Reproduction

[ResourceCreate (OK)](https://typespec.io/playground/?c=aW1wb3J0ICJAdHlwZXNwZWMvaHR0cCI7CtIZcmVzdCI7CgpAc2VydmljZSh7CiAgdGl0bGU6ICJXaWRnZXQgU8YbIiwKfSkKbmFtZXNwYWNlIERlbW%2FHGzsKCnVzaW5nIFR5cGVTcGVjLkh0dHA70BVSZXN0OwoKbW9kZWwgx13EcEBrZXkgaWQ6IHN0cmluZzsKICB3ZWlnaHQ6IGludDMyxBFjb2xvcjogInJlZCIgfCAiYmx1ZSI7Cn0KCkBlcnJvcsdWRmlyc3RFxBHGWnN0YXR1c0NvZGUgXzogNDAzxExtZXNzYWdlynDQRlNlY29uZNtHMNhHaW50ZXJm5AEf5gDg5wEhIGV4dGVuZHMgUmVzb3VyY2XkAQzFCUNyZWF0ZTzGLizsAMB87ACHPiB7fQo%3D&e=%40typespec%2Fopenapi3&options=%7B%22linterRuleSet%22%3A%7B%22extends%22%3A%5B%22%40typespec%2Fhttp%2Fall%22%5D%7D%7D)

[ResourceUpdate (Error)](https://typespec.io/playground/?c=aW1wb3J0ICJAdHlwZXNwZWMvaHR0cCI7CtIZcmVzdCI7CgpAc2VydmljZSh7CiAgdGl0bGU6ICJXaWRnZXQgU8YbIiwKfSkKbmFtZXNwYWNlIERlbW%2FHGzsKCnVzaW5nIFR5cGVTcGVjLkh0dHA70BVSZXN0OwoKbW9kZWwgx13EcEBrZXkgaWQ6IHN0cmluZzsKICB3ZWlnaHQ6IGludDMyxBFjb2xvcjogInJlZCIgfCAiYmx1ZSI7Cn0KCkBlcnJvcsdWRmlyc3RFxBHGWnN0YXR1c0NvZGUgXzogNDAzxExtZXNzYWdlynDQRlNlY29uZNtHMNhHaW50ZXJm5AEf5gDg5wEhIGV4dGVuZHMgUmVzb3VyY2XkAQzFCVVwZGF0ZTzGLizsAMB87ACHPiB7fQo%3D&e=%40typespec%2Fopenapi3&options=%7B%22linterRuleSet%22%3A%7B%22extends%22%3A%5B%22%40typespec%2Fhttp%2Fall%22%5D%7D%7D)

### Checklist

- [x] Follow our [Code of Conduct](https://github.com/microsoft/typespec/blob/main/CODE_OF_CONDUCT.md)
- [x] Check that there isn't already an issue that request the same bug to avoid creating a duplicate.
- [x] Check that this is a concrete bug. For Q&A open a [GitHub Discussion](https://github.com/Microsoft/typespec/discussions).
- [x] The provided reproduction is a [minimal reproducible example](https://stackoverflow.com/help/minimal-reproducible-example) of the bug.