Pin GitHub workflows to rc.1 SDK (#871)

* Pin GitHub workflows to rc.1 SDK

* Make src/* change to force PR tests

* Add global.json to paths that trigger PR tests

.github/workflows/ci-build-test.yml

@@ -15,6 +15,7 @@ on:
       - "*.sln"
       - "*.props"
       - "Makefile"
+      - "global.json"
       - "src/**"
       - "tests/**"
       - "samples/**"
@@ -43,7 +44,7 @@ jobs:
       uses: actions/setup-dotnet@d4c94342e560b34958eacfc5d055d21461ed1c5d # v5.0.0
       with:
         dotnet-version: |
-          10.0.x
+          10.0.100-rc.1.25451.107
           9.0.x
 
     # NetFX testing on non-Windows requires mono