[release plan] A new release plan should not be created if the spec PR doesn't introduce a new API version

Related release plan: https://azsdk-releaseplan-dashboard-hveph5aqhhcfhtgu.westus-01.azurewebsites.net/?releaseplan=36354
Spec PR: https://github.com/Azure/azure-rest-api-specs/pull/45760

There are only some .NET related changes in the spec PR, but a release plan of 2026-05-01-preview was created after this PR was merged which is not expected. According to the guidance https://eng.ms/docs/products/azure-developer-experience/plan/release-plan-create, a release plan should be generated only when the spec PR adds a new API version.

More context: the packages of other languages were already released with https://azsdk-releaseplan-dashboard-hveph5aqhhcfhtgu.westus-01.azurewebsites.net/?releaseplan=2241, and only .NET needs to be released this time.