Fix pkg-name in find_package_handle_standard_args

[Krzmbrzl]

For the MySQL package find_package_handle_standard_args got passed "MYSQL" as the package name, which differs from
the actual package name. Due to this cmake (3.18) emitted a warning.
This commit fixes this issue by also passing "MySQL" to find_package_handle_standard_args.

Fixes #3066

[Bjoe]

But still the question is, should we also "camel-case" the other Variable Names?
See https://cmake.org/cmake/help/latest/manual/cmake-developer.7.html#standard-variable-names

But this will break others build system. Maybe rename FindMySQL.cmake to FindMYSQL.cmake and add a FindMySQL.cmake and give a warning that this is deprecated and they should use FindMYSQL.cmake ?

[Krzmbrzl]

But still the question is, should we also "camel-case" the other Variable Names?
See cmake.org/cmake/help/latest/manual/cmake-developer.7.html#standard-variable-names

Yeah that'd probably have to be done as well 🤔

But this will break others build system. Maybe rename FindMySQL.cmake to FindMYSQL.cmake and add a FindMySQL.cmake and give a warning that this is deprecated and they should use FindMYSQL.cmake ?

By renaming the FindMYSQL, it should not interfere with any project using poco, should it? In that case I don't even see the need for providing a FindMySQL at all 👀

[obiltschnig]

Leaving it at FindMySQL.cmake for now, as we have the same issue with PostgreSQL.