Fix: Use safeBeat in push monitor

[chakflying]

⚠️⚠️⚠️ Since we do not accept all types of pull requests and do not want to waste your time. Please be sure that you have read pull request rules:
https://github.com/louislam/uptime-kuma/blob/master/CONTRIBUTING.md#can-i-create-a-pull-request-for-uptime-kuma

Tick the checkbox if you understand [x]:

• I have read and understand the pull request rules.

Description

Fixes #3130

Normally, a monitor is able to "heal" itself following an error because of the use of safeBeat. Following investigation in #3130, error in push monitor causes the monitor to fail and not restart. Switching to safeBeat solves the issue. I tested this by adding to Math.random() call to throw error after saving to database.

Type of change

• Bug fix (non-breaking change which fixes an issue)

Checklist

• My code follows the style guidelines of this project
• I ran ESLint and other linters for modified files
• I have performed a self-review of my own code and tested it
• I have commented my code, particularly in hard-to-understand areas
  (including JSDoc for methods)
• My changes generate no new warnings
• My code needed automated testing. I have added them (this is optional task)

Screenshots (if any)

Please do not use any external image service. Instead, just paste in or drag and drop the image here, and it will be uploaded automatically.

[CommanderStorm]

Could you please go into detail how you tested this PR? I am unclear what you added where to test it.

Do you think this case would make a good unittest to prevent regressions in the future?