Export $FLEPI_PATH in GH action

Set the `$FLEPI_PATH` environment variable in the gempyor CI GitHub
action, because the internal `gempyor.info._get_info` function needs it
to know where to look for config YAMLs.

.github/workflows/gempyor-ci.yml

@@ -49,6 +49,7 @@ jobs:
         shell: bash
       - name: Run gempyor tests
         run: |
+          export FLEPI_PATH=$(pwd)
           cd flepimop/gempyor_pkg
           pytest --exitfirst
         shell: bash