Update github action readme parsing

Author: Clorith

.github/workflows/trunk-release-tag.yml

@@ -55,7 +55,7 @@ jobs:
       - name: Get changelog entries
         id: changelog
         working-directory: ./docs
-        run: echo '::set-output name=changes::{grep -A100 -m1 -e '== Changelog ==' readme.txt}'
+        run: echo "::set-output name=changes::$(grep -A100 -m1 -e '== Changelog ==' readme.txt)"
 
       - name: Create release
         id: create_release