Only `$penv{}` can be expanded when processing includes.

We know the encoding of the schema file, so we should specify it
when we open it for reading. Previously, by not specifying it, the test
was open to using an encoding based on the active locale when
running the test. We may have been enforcing a "C" locale at a higher
level, but we don't need to rely on that here, we can force correct
behavior without that assumption.

Issue: #24679

Add JSON schema version 7 to support them.

Fixes: #22543

Fixes: #23118

Only print an extra newline after a section if that section was
actually printed.

Tweak test in RunCMake/CMakePresets/GoodNoSCache.cmake to use the
canonical directory for comparison. This avoids an effectively spurious
test failure if the overall CMake build directory is a symlink.