Change Python version from 3.13 to 3.9

Author: realybin

.github/workflows/unity_unittest.yml

@@ -123,7 +123,7 @@ jobs:
           dotnet-version: '6.x.x'
       - uses: actions/setup-python@v5
         with:
-          python-version: '3.13' 
+          python-version: '3.9' 
       - uses: actions/checkout@v3
       - name: UnitTest-v8
         run: |
@@ -203,4 +203,4 @@ jobs:
       - name: UnitTest-v8-ts
         run: |
           cd unity/test/dotnet
-          node ../../cli dotnet-test -ts
+          node ../../cli dotnet-test -ts