Add repro for rollup/rollup#4995.

README.md

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+### Goal
+
+Demonstrate / reproduce the issue reported in https://github.com/rollup/rollup/issues/4995.
+
+### Prerequisites
+
+`node` and `npx` need to be installed.
+
+First do an `npm install`.
+
+### How-To
+
+The issue can be reproduced both exec both of `@actions/exec` and `child_process`. The node scripts each use the respective `exec` function to invoke [test.sh](test.sh). The bash script uses `npx` to invoke _rollup_, first v3.21.5 (OK), then v3.21.6 (NOK). After that second invocation, the subsequent `echo` fails.
+
+@actions/exec:
+
+```
+node actions.js
+```
+
+child_process:
+
+```
+node child_process.js
+```
+
+### Errors
+
+@actions/exec:
+
+```
+Error occurred during test.sh: Error: The process '/bin/bash' failed with exit code null
+    at ExecState._setResult (/Users/manu/incon.ai/rollup-stdout-repro/node_modules/@actions/exec/lib/toolrunner.js:592:25)
+    at ExecState.CheckComplete (/Users/manu/incon.ai/rollup-stdout-repro/node_modules/@actions/exec/lib/toolrunner.js:575:18)
+    at ChildProcess.<anonymous> (/Users/manu/incon.ai/rollup-stdout-repro/node_modules/@actions/exec/lib/toolrunner.js:469:27)
+    at ChildProcess.emit (node:events:513:28)
+    at maybeClose (node:internal/child_process:1091:16)
+    at Socket.<anonymous> (node:internal/child_process:449:11)
+    at Socket.emit (node:events:513:28)
+    at Pipe.<anonymous> (node:net:322:12)
+```
+
+child_process:
+
+```
+Error occurred during test.sh: Error: Command failed: bash test.sh
+[...]
+    at ChildProcess.exithandler (node:child_process:419:12)
+    at ChildProcess.emit (node:events:513:28)
+    at maybeClose (node:internal/child_process:1091:16)
+    at Socket.<anonymous> (node:internal/child_process:449:11)
+    at Socket.emit (node:events:513:28)
+    at Pipe.<anonymous> (node:net:322:12) {
+  code: null,
+  killed: false,
+  signal: 'SIGPIPE',
+  cmd: 'bash test.sh'
+}
+```

actions.js

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+const { exec } = require('@actions/exec');
+
+async function test() {
+  try {
+    await exec('bash test.sh');
+    console.log('test.sh completed successfully!');
+  } catch (error) {
+    console.error('Error occurred during test.sh:', error);
+  }
+}
+
+test();

child_process.js

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+const { exec } = require('child_process');
+
+function test() {
+  exec('bash test.sh', (error, stdout, stderr) => {
+    if (error) {
+      console.error('Error occurred during test.sh:', error);
+    } else {
+      console.log('test.sh completed successfully!');
+    }
+    if (stdout) {
+      console.log('test.sh output:', stdout);
+    }
+    if (stderr) {
+      console.error('test.sh error output:', stderr);
+    }
+  });
+}
+
+test();

package.json

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+{
+  "name": "nodetest",
+  "version": "1.0.0",
+  "description": "",
+  "main": "actions.js",
+  "scripts": {
+    "test": "echo \"Error: no test specified\" && exit 1"
+  },
+  "keywords": [],
+  "author": "",
+  "dependencies": {
+    "@actions/exec": "^1.1.1"
+  }
+}

rollup.config.js

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+module.exports = {
+  input: 'actions.js',
+  output: {
+    file: 'dist/bundle.js',
+    format: 'es',
+  },
+};

test.sh

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+echo "before"
+
+npx rollup@3.21.5 -c
+
+echo "between"
+
+npx rollup@3.21.6 -c
+
+echo "after"