[actions] Fix parsing problem in the changelog action. (#16940)

Fixes this:

    SyntaxError: Unexpected identifier
        at new AsyncFunction (<anonymous>)
    Error: Unhandled error: SyntaxError: Unexpected identifier
        at callAsyncFunction (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:13356:16)
        at main (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:13452:26)
        at Module.858 (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:13429:1)
        at __webpack_require__ (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:24:31)
        at startup (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:43:19)
        at /home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:49:18
        at Object.<anonymous> (/home/runner/work/_actions/actions/github-script/v6.3.3/dist/index.js:52:10)
        at Module._compile (node:internal/modules/cjs/loader:1101:14)
        at Object.Module._extensions..js (node:internal/modules/cjs/loader:1153:10)

by not storing the changelog entry in an environment variable between tasks,
but instead store it on disk.

.github/workflows/maestro-changelog.yml

@@ -16,20 +16,20 @@ jobs:
         dotnet run https://github.com/$GITHUB_REPOSITORY/pull/${GITHUB_REF_NAME/\/*/} > changelog.txt 2>&1
 
         # need to replace newlines with actual "\n"
-        rm -f changelog2.txt
-        echo "CHANGELOG_MESSAGE<<EOF" >> changelog2.txt
-        cat changelog.txt | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/\\n/g' >> changelog2.txt
-        echo EOF >> changelog2.txt
-        cat changelog2.txt
+        CHANGELOG_FILE=changelog2.txt
+        rm -f "$CHANGELOG_FILE"
+        cat changelog.txt | sed -e ':a' -e 'N' -e '$!ba' -e 's/\n/\\n/g' >> "$CHANGELOG_FILE"
+        cat "$CHANGELOG_FILE"
 
-        # export the changelog message
-        cat changelog2.txt >> $GITHUB_ENV
+        cp "$CHANGELOG_FILE" /tmp/changelog.txt
 
     - name: 'Add changelog'
       uses: actions/github-script@v6.3.3
       with:
         github-token: ${{secrets.GITHUB_TOKEN}}
         script: |
+          const fs = require('fs');
+          const changelog_message = fs.readFileSync('/tmp/changelog.txt', 'utf8');
           // check if we've already added a changelog to this PR, and if so, update that comment, otherwise add a new comment
           var commentId = ""
           await github.paginate (github.rest.issues.listComments,
@@ -48,13 +48,13 @@ jobs:
               owner: context.repo.owner,
               repo: context.repo.repo,
               issue_number: context.issue.number,
-              body: '${{ env.CHANGELOG_MESSAGE }}'
+              body: changelog_message
             })
           } else {
             github.rest.issues.updateComment({
               owner: context.repo.owner,
               repo: context.repo.repo,
               comment_id: commentId,
-              body: '${{ env.CHANGELOG_MESSAGE }}'
+              body: changelog_message
             })
           }