[PR Validation] Let markers checker match marker from whole text instead of single line

[w1nda]

Description of PR

Summary:
Fixes # (issue)
In PR #16069, the PR validation pipeline failed on error: Please add mark pytest.mark.topology in script bgp/test_ipv6_bgp_scale.py.

After debugging, I found that the pipeline match the pattern per line, so it will not match the marker in format:

pytestmark = [
    pytest.mark.topology(
        't0-isolated-d2u254s1', 't0-isolated-d2u254s2', 't0-isolated-d2u510',
        't1-isolated-d254u2s1', 't1-isolated-d254u2s2', 't1-isolated-d510u2'
    )
]

However, If I write all mark in same line, it will exceed the maximum line length, so I raise this PR to let mark checker match pattern from whole script instead of lines.

Type of change

• Bug fix
• Testbed and Framework(new/improvement)
• New Test case
  • Skipped for non-supported platforms
• Test case improvement

Back port request

• 202012
• 202205
• 202305
• 202311
• 202405
• 202411

Approach

What is the motivation for this PR?

In summary section.

How did you do it?

let mark checker match pattern from whole script instead of lines.

How did you verify/test it?

1. trigger pipeline by this PR.
2. run script locally.

Any platform specific information?

NA

Supported testbed topology if it's a new test case?

Documentation

[mssonicbld]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).