Update ci.yml for 3.6.8 (macOs)

Author: dalehenrich

.github/workflows/ci.yml

@@ -16,7 +16,7 @@ jobs:
         os: [ ubuntu-20.04 ]
         smalltalk: [ GemStone64-3.7.0, GemStone64-3.6.8, GemStone64-3.5.8 ]
         include: 
-          - smalltalk: GemStone64-3.6.7
+          - smalltalk: GemStone64-3.6.8
             os: macos-latest
           - smalltalk: GemStone64-3.5.8
             os: macos-latest