regex warnings in MsftLinuxPatchCore.py?

**Describe the bug**
I see the following in my journalctl logs:

```
Aug 22 00:36:41 sr-monitor systemd[1]: Starting MsftLinuxPatchAutoAssess.service - Microsoft Azure Linux Patch Extension - Auto Assessment...
Aug 22 00:36:41 sr-monitor bash[143561]: /var/lib/waagent/Microsoft.CPlat.Core.LinuxPatchExtension-1.6.62/MsftLinuxPatchCore.py:7451: SyntaxWarning: invalid escape sequence '\_'
Aug 22 00:36:41 sr-monitor bash[143561]: """ Fetches pid from the error message by searching for the text 'pid' and returns the process tree with all details.
Aug 22 00:36:41 sr-monitor bash[143561]: /var/lib/waagent/Microsoft.CPlat.Core.LinuxPatchExtension-1.6.62/MsftLinuxPatchCore.py:7468: SyntaxWarning: invalid escape sequence '\d'
Aug 22 00:36:41 sr-monitor bash[143561]: regex = re.compile(' pid \d+')
Aug 22 00:36:41 sr-monitor bash[143561]: /var/lib/waagent/Microsoft.CPlat.Core.LinuxPatchExtension-1.6.62/MsftLinuxPatchCore.py:7476: SyntaxWarning: invalid escape sequence '\d'
Aug 22 00:36:41 sr-monitor bash[143561]: regex = re.compile('\d+')
```

Is this a bug?

**To Reproduce**
Steps to reproduce the behavior:
1. Create Azure Ubuntu VM
2. Enable LinuxPatchExtension
3. Watch the logs

**Expected behavior**
No regex warnings

**Screenshots**
If applicable, add screenshots to help explain your problem.

**Desktop (please complete the following information):**
- OS: ubuntu
- Browser N/A
- Version 24_04-lts

**Smartphone (please complete the following information):**
- Device: [e.g. iPhone6]
- OS: [e.g. iOS8.1]
- Browser [e.g. stock browser, safari]
- Version [e.g. 22]

**Additional context**
Add any other context about the problem here.

从 MsftLinuxPatchCore.py 的第 7451、7468 和 7476 行开始，然后在 Ubuntu 24.04 Azure VM 上重现该问题，同时观察扩展日志。验证受影响的 regex 处理在 LinuxPatchExtension 启动期间不再发出无效转义序列警告。

由索引模型根据 Issue 内容生成。