test: fix os-release check for Ubuntu in SEA test

For example, my `/etc/os-release` file begins with

```
PRETTY_NAME="Ubuntu 22.04.2 LTS"
NAME="Ubuntu"
VERSION_ID="22.04"
```

so in order to match the regexp here, the `/m` flag is necessary.

PR-URL: #46838
Reviewed-By: Moshe Atlow <[email protected]>
Reviewed-By: Tobias Nießen <[email protected]>
Reviewed-By: Darshan Sen <[email protected]>
Reviewed-By: Luigi Pinca <[email protected]>

Author: addaleax

test/parallel/test-single-executable-application.js

@@ -41,7 +41,7 @@ if (process.config.variables.want_separate_host_toolset !== 0)
 if (process.platform === 'linux') {
   try {
     const osReleaseText = readFileSync('/etc/os-release', { encoding: 'utf-8' });
-    if (!/^NAME="Ubuntu"/.test(osReleaseText)) {
+    if (!/^NAME="Ubuntu"/m.test(osReleaseText)) {
       throw new Error('Not Ubuntu.');
     }
   } catch {