[policyinsights] autorest fails to generate openapi documents from input config and files

`autorest` fails to generate output documents from the `policyinsights` specification

running:
```
autorest ./resource-manager/readme.md \
--openapi-type=arm \
--output-converted-oai3
```
from the `azure-rest-api-specs/specification/policyinsights` directory

yields the following non descript error:

```
fatal | Process() cancelled due to failure
error | TypeError [ERRINVALIDURL]: Invalid URL
error | Autorest completed with an error. If you think the error message is unclear, or is a bug, please declare an issues at https://github.com/Azure/autorest/issues with the error message you are seeing.
```
all other services in the `specification` directory work with the same command

Start in specification/policyinsights/resource-manager/readme.md and reproduce the documented autorest command from the policyinsights directory. Compare the result with other service specifications that use the same command; done means the policyinsights specification generates output documents without the Invalid URL error.

Written by the indexing model from the issue text.