ci.yaml: Pin pathogen-repo-ci

Pin the `pathogen-repo-ci` to v0, which is before changes for the
"smart" workflow were added.

Author: joverlee521

.github/workflows/ci.yaml

@@ -9,4 +9,4 @@ on:
 
 jobs:
   pathogen-ci:
-    uses: nextstrain/.github/.github/workflows/pathogen-repo-ci.yaml@master
+    uses: nextstrain/.github/.github/workflows/pathogen-repo-ci.yaml@v0