ci: check lambdapi 2.6.0

Author: fblanqui

.github/workflows/main.yml

@@ -8,7 +8,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        lambdapi-version: [lambdapi] #,lambdapi.2.5.1,lambdapi.2.5.0,lambdapi.2.4.1,lambdapi.2.4.0,lambdapi.2.3.1]
+        lambdapi-version: [lambdapi,lambdapi.2.6.0] #,lambdapi.2.5.1,lambdapi.2.5.0,lambdapi.2.4.1,lambdapi.2.4.0,lambdapi.2.3.1]
     runs-on: ubuntu-latest
     steps:
       - name: Check out library