BLD: Correct gcsfs install on Azure
Follow-up #26352

Also realized that the `gcsfs` install was placed in the wrong place (needs to be placed after the `activate` command).  However, you will notice then that the install is the culprit for the earlier 3.7 build failures (something is not right on `conda-forge` and / with `gcsfs` and `3.7`).  Note though that the install of `gcsfs` works just fine on `3.6`.