Simplify test implementation for ProjectTemplates

What does this MR do?

Closes #219189 (closed)

Problem

Tests for project templates validate only name and title of ProjectTemplate, other parameters are ignored even if we provide them.

Solution

One option would be to add extra validation for description, URLs, and icons. But I don't think that it brings enough value. I assume that people add a new project template to the test suite by copy-and-pasting its name, title, and description from the original ProjectTemplate's definition. If the definition has a typo then most probably it will be copy-and-pasted to the test suite.

I think it makes sense to check only that we've properly defined the project template. For that, we can validate if .all returns the name of the project template in the list. I think it should be sufficient and it simplifies the test setup.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

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• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
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