ci: Correct versions file path in release workflow (shaka-project#47)

This was mistaken ever since we moved the file, but we haven't made any
releases since then. The effect of this bug would be to have the
"versions" section of the release notes be empty.

.github/workflows/release.yaml

@@ -95,7 +95,7 @@ jobs:
           echo "" >> body.txt
 
           echo "Software versions:" >> body.txt
-          cat repo-src/.github/workflows/versions.txt | \
+          cat repo-src/versions.txt | \
             sed -e 's/^/ - /' >> body.txt
           echo "" >> body.txt