CI: Migrate slow test suit from Travis CI

Signed-off-by: Jessica Wagantall <[email protected]>

Author: jwagantall

.github/workflows/tests.yml

@@ -31,6 +31,7 @@ jobs:
         suite:
           - install_script
           - sourcing
+          - slow
         shell:
           - sh
           - bash

.travis.yml

@@ -87,11 +87,6 @@ env:
     - SHELL=bash TEST_SUITE=fast
     - SHELL=zsh TEST_SUITE=fast
     #  - SHELL=ksh TEST_SUITE=fast
-    - SHELL=sh TEST_SUITE=slow
-    - SHELL=dash TEST_SUITE=slow
-    - SHELL=bash TEST_SUITE=slow
-    - SHELL=zsh TEST_SUITE=slow
-    #  - SHELL=ksh TEST_SUITE=slow
     - SHELL=sh TEST_SUITE=installation_iojs
     - SHELL=sh TEST_SUITE=installation_iojs WITHOUT_CURL=1
     - SHELL=dash TEST_SUITE=installation_iojs