Export the ET_VERSION_DOCS variable in doc build (#3358)

Summary: Pull Request resolved: #3358

Reviewed By: dbort

Differential Revision: D56584847

Pulled By: svekars

fbshipit-source-id: 77c4105edf15503bf1b29c1f120111a73b973c4c
(cherry picked from commit c32b0a2)

Author: svekars

.github/workflows/doc-build.yml

@@ -49,7 +49,7 @@ jobs:
 
         GITHUB_REF=${{ github.ref }}
         echo "$GITHUB_REF"
-        ET_VERSION_DOCS="${GITHUB_REF}"
+        export ET_VERSION_DOCS="${GITHUB_REF}"
         echo "$ET_VERSION_DOCS"
 
         set -eux