chore: fix multiline string variable in workflow [skip ci]

.github/workflows/upgrade-dependencies.yaml

@@ -15,14 +15,17 @@ jobs:
         uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29 # v4.1.6
       - name: Install
         run: yarn install
-      - name: Get the output from yarn outdated and save it in a variable to reference in the PR body
-        id: yarn
-        run: |-
+      - name: Get the output from yarn outdated and save it in an environment variable
+        # See: https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#multiline-strings
+        run: |
           {
-            echo 'outdated<<EOF'
+            echo 'YARN_OUTDATED<<EOF'
             yarn outdated
             echo EOF
-          } >> "$GITHUB_OUTPUT"
+          } >> "$GITHUB_ENV"
+      - name: Take the env var from the previous step and save it in an output variable to reference in the PR body
+        id: yarn
+        run: echo "outdated=$YARN_OUTDATED" >> $GITHUB_OUTPUT
       - name: Do the upgrade
         run: yarn upgrade
       - name: Create Pull Request