ci: switches to hidi preview to both dogfood and avoid flakly NRE

Author: baywet

.github/workflows/metadata-parser-validation.yml

@@ -36,7 +36,7 @@ jobs:
       with:
         dotnet-version: 9.x
 
-    - run: dotnet tool install --global Microsoft.OpenApi.Hidi
+    - run: dotnet tool install --global Microsoft.OpenApi.Hidi --version 2.0.0-preview.29
       name: Install  Hidi
 
     - name: Validate latest XSLT rules

.github/workflows/openapi-parser-validation.yml

@@ -36,7 +36,7 @@ jobs:
       with:
         dotnet-version: 9.x
 
-    - run: dotnet tool install --global Microsoft.OpenApi.Hidi
+    - run: dotnet tool install --global Microsoft.OpenApi.Hidi --version 2.0.0-preview.29
       name: Install  Hidi
 
     - name: Validate latest OpenAPI docs