Allow failure of slc6 lcg95 builds

Until #632 (closed) is resolved we'll allow the problematic jobs to fail.

.gitlab-ci.yml

@@ -175,6 +175,7 @@ build_slc6_lcg95:
   image: gitlab-registry.cern.ch/acts/machines/slc6:latest
   before_script:
     - set +e && source CI/setup_lcg95.sh; set -e
+  allow_failure: true
 
 unit_tests_slc6_lcg95:
   <<: *template_unit_tests
@@ -193,6 +194,7 @@ unit_tests_slc6_lcg95:
   artifacts:
     paths:
       - build/coverage
+  allow_failure: true
 
 integration_tests_slc6_lcg95:
   <<: *template_integration_tests
@@ -201,6 +203,7 @@ integration_tests_slc6_lcg95:
   image: gitlab-registry.cern.ch/acts/machines/slc6:latest
   before_script:
     - set +e && source CI/setup_lcg95.sh; set -e
+  allow_failure: true
 
 # SLC, LCG94, LLVM60