Fixes cpp_info.name vs. cpp_info.names issue in pkg_config generator

[danimtb]

Changelog: Bugfix: Fixes cpp_info.name vs. cpp_info.names issue in pkg_config generator
Docs: omit

TARGET THIS TO NEW RELEASE BRANCH Done!

• Refer to the issue that supports this Pull Request: closes pkg_config generator: fix case handling #6211 closes [bug] pkg_config generator has wrong casing in the requires section #6222
• If the issue has missing info, explain the purpose/use case/pain/need that covers this Pull Request.
• I've read the Contributing guide.
• I've followed the PEP8 style guides for Python code.
• I've opened another PR in the Conan docs repo to the develop branch, documenting this one.

^{Note: By default this PR will skip the slower tests and will use a limited set of python versions. Check here how to increase the testing level by writing some tags in the current PR body text.}

[ericLemanissier]

That should do it

[jgsogo]

There is a new branch release/1.21.1, this PR should be changed to target that one.

[danimtb]

Done!