CMake 3.27 deprecates compatibility with CMake < 3.5.  Update tests that
do not cover older interfaces to avoid the deprecation warning.

Follow the pattern from:

* commit 7b07ccdd2b (Tests/*Only: Update cmake_minimum_required versions,
                     2020-06-15, v3.19.0-rc1~629^2~1)

* commit 72e7c45e98 (Tests: Bump CMake minimum required in tests to 2.8.12,
                     2020-12-22, v3.20.0-rc1~224^2)

* commit f6b4db365a (Tests: bump cmake_minimum_required version to 2.8.12,
                     2021-04-04, v3.21.0-rc1~372^2)

Also remove explicit `cmake_policy` settings made redundant by the
version.

Since 3.19, CMake generates a deprecation warning when using a minimum
version less than 2.8.12.  This eliminates those warnings generated
during tests, which are typically hidden from the user and developer but
are being generated nonetheless.

Commit 79568f95 (automoc: Add source file to target early to set the
linker language, 2013-02-20) changed automoc initialization to a two
step process. In the first step, the generated source file was added
to the target, which allows the link language to be determined.

However, this bypassed the check for the availability of Qt itself.
At build-time the automoc file could not be generated because the moc
tool was not available to create it.

The solution is to only add the automoc file to the target if Qt is
found.