Fixes malformed string input for stale announce workflow (#95823)

## About The Pull Request
Fixes https://github.com/tgstation/tgstation/actions/runs/24643489491
Fixes https://github.com/tgstation/tgstation/actions/runs/24058690318

Storing the string as environment variable removes the need to runtime
decode the value which causes double slashes // to be decoded as a
single slash / which breaks the json string

## Changelog
N/A

.github/workflows/stale.yml

@@ -38,9 +38,11 @@ jobs:
       - name: Filter staled pull requests for announcement
         id: filter-prs
         uses: actions/github-script@v9
+        env:
+          input: ${{steps.stale.outputs.staled-issues-prs}}
         with:
           script: |
-            return JSON.parse(`${{steps.stale.outputs.staled-issues-prs}}`)
+            return JSON.parse(process.env.input)
                        .filter(issue => !!issue.pull_request)
                        .map(pr => ({
                         title: pr.title,