⬇️back to version 1.25.4 for CI tests (stable = 1.26 doesn't seem to work)

Author: Tesshub

.github/workflows/build.yaml

@@ -20,7 +20,7 @@ jobs:
       - name: "Set up OpenModelica Compiler"
         uses: OpenModelica/setup-openmodelica@v1.0.5
         with:
-          version: 'stable'
+          version: '1.25.4'
           packages: |
             'omc'
             'omsimulator'