Update CLI integration tests with latest version of CLI (#889)

CodeQL CLI v2.5.6 was released yesterday 🎉

.github/workflows/main.yml

@@ -127,7 +127,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest, windows-latest]
-        version: ['v2.2.6', 'v2.3.3', 'v2.4.6', 'v2.5.5']
+        version: ['v2.2.6', 'v2.3.3', 'v2.4.6', 'v2.5.6']
     env:
       CLI_VERSION: ${{ matrix.version }}
       TEST_CODEQL_PATH: '${{ github.workspace }}/codeql'