Improve CMake and Actions settings

[doug-walker]

Several minor build fixes:

• Fix a CMake error in how OCIO_NAMESPACE was being used. This was discussed at the TSC meeting and the preference was for this to continue to be the full string that is used. Therefore, cleaning up some code that was incorrectly using it as part of a longer string.
• Reducing the frequency of Dependabot PRs and requesting only security fixes. Currently it seems to be proposing fixes for minor version increases that have no security aspect.
• Fix documentation comment that was causing a build failure on Windows.

[remia]

Thanks for fixing the Windows documentation issue Doug, I saw this in my PR too.

[doug-walker]

Will go ahead and merge this since Analysis runs never succeed on PRs.