add Pharo9.0 in CI

Author: SergeStinckwich

.github/workflows/smalltalk-ci.yml

@@ -15,7 +15,7 @@ jobs:
     strategy:
       matrix:
         os: [ macos-latest, windows-latest, ubuntu-latest]
-        smalltalk: [ Pharo64-8.0 ]
+        smalltalk: [ Pharo64-8.0 Pharo64-9.0]
     runs-on: ${{ matrix.os }}
     name: ${{ matrix.smalltalk }} on ${{ matrix.os }}
     steps: