check_changeset.ts: use writeFile() to write the CHANGESET_ERROR_MESSAGE to $GITHUB_OUTPUT instead of echo since embedded quotes in the error message cause the shell to mis-interpret them

For example, in https://github.com/firebase/firebase-js-sdk/actions/runs/7586489122/job/20664769245?pr=7952 the following error occurred, which this commit fixes:

```
$ /home/runner/work/firebase-js-sdk/firebase-js-sdk/node_modules/.bin/ts-node-script scripts/ci/check_changeset.ts
/home/runner/work/firebase-js-sdk/firebase-js-sdk/node_modules/child-process-promise/lib/index.js:33
            var cpError = new ChildProcessError(err.message, err.code, child_process, stdout, stderr);
                          ^
ChildProcessError: Command failed: echo "CHANGESET_ERROR_MESSAGE=- Changeset formatting error in following file:%0A    \`\`\`%0A    Some packages have been changed but no changesets were found. Run \`changeset add\` to resolve this error.%0A    If this change doesn't need a release, run \`changeset add --empty\`.%0A    \`\`\`%0A" >> $GITHUB_OUTPUT
/bin/sh: 1: Syntax error: Unterminated quoted string
 \`echo "CHANGESET_ERROR_MESSAGE=- Changeset formatting error in following file:%0A    \`\`\`%0A    Some packages have been changed but no changesets were found. Run \`changeset add\` to resolve this error.%0A    If this change doesn't need a release, run \`changeset add --empty\`.%0A    \`\`\`%0A" >> $GITHUB_OUTPUT\` (exited with error code 2)
    at callback (/home/runner/work/firebase-js-sdk/firebase-js-sdk/node_modules/child-process-promise/lib/index.js:33:27)
    at ChildProcess.exithandler (node:child_process:410:5)
    at ChildProcess.emit (node:events:513:28)
    at ChildProcess.emit (node:domain:489:12)
    at maybeClose (node:internal/child_process:1100:16)
    at Socket.<anonymous> (node:internal/child_process:458:11)
    at Socket.emit (node:events:513:28)
    at Socket.emit (node:domain:489:12)
    at Pipe.<anonymous> (node:net:301:12) {
  code: 2,
  childProcess: {
    _forkChild: [Function: _forkChild],
    ChildProcess: [Function: ChildProcess],
    exec: [Function: exec],
    execFile: [Function: execFile],
    execFileSync: [Function: execFileSync],
    execSync: [Function: execSync],
    fork: [Function: fork],
    spawn: [Function: spawn],
    spawnSync: [Function: spawnSync]
  },
  stdout: '',
  stderr: '/bin/sh: 1: Syntax error: Unterminated quoted string\n'
}
error Command failed with exit code 1.
```

Author: dconeybe

scripts/ci/check_changeset.ts

@@ -17,6 +17,7 @@
 
 import { resolve } from 'path';
 import { existsSync } from 'fs';
+import { writeFile } from 'fs/promises';
 import { exec } from 'child-process-promise';
 import chalk from 'chalk';
 import simpleGit from 'simple-git';
@@ -28,6 +29,14 @@ const git = simpleGit(root);
 const baseRef = process.env.GITHUB_PULL_REQUEST_BASE_SHA || 'master';
 const headRef = process.env.GITHUB_PULL_REQUEST_HEAD_SHA || 'HEAD';
 
+const githubOutputFile = (function (): string {
+  const value = process.env.GITHUB_OUTPUT;
+  if (!value) {
+    throw new Error('GITHUB_OUTPUT environment variable must be set');
+  }
+  return value;
+})();
+
 // Version bump text converted to rankable numbers.
 const bumpRank: Record<string, number> = {
   'patch': 0,
@@ -205,10 +214,13 @@ async function main() {
    * step. See:
    * https://docs.github.com/en/actions/using-workflows/workflow-commands-for-github-actions#setting-an-output-parameter
    */
-  if (errors.length > 0)
-    await exec(
-      `echo "CHANGESET_ERROR_MESSAGE=${errors.join('%0A')}" >> $GITHUB_OUTPUT`
+  if (errors.length > 0) {
+    await writeFile(
+      githubOutputFile,
+      `CHANGESET_ERROR_MESSAGE=${errors.join('%0A')}\n`,
+      { flag: 'a' }
     );
+  }
   process.exit();
 }