Make opentelemetry-test-utils tests more robust to error format

[musicinmybrain]

Description

Adapts opentelemetry-test-utils for Python 3.13 improved error messages by making TestAssertNotRaises.test_missing_exception insensitive to the exact line numbers of expected text within the error message.

Fixes #3953.

Type of change

Please delete options that are not relevant.

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

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

$ tox -e py313-opentelemetry-test-utils
$ tox -e py312-opentelemetry-test-utils

Does This PR Require a Contrib Repo Change?

• [ ] Yes. - Link to PR:
• [x] No.

Checklist:

• [x] Followed the style guidelines of this project
• [ ] Changelogs have been updated Is this needed?
• [ ] Unit tests have been added N/A
• [ ] Documentation has been updated N/A