Fix compile issue in OutofcoreOctreeBase::setLODFilter after switching from boost::shared_ptr to std::shared_ptr

[SunBlack]

Fixes #4033.

Short explanation: Since #3750 we are using std::shared_ptr instead of boost::shared_ptr and it seems automatic downcasting does not work there anymore.

[kunaltyagi]

If we were using clang on the CI, we would have caught this, right?

[SunBlack]

Possible, just tested it with Clang 10 - not sure if older Clang version also complains it. In general Clang is more restrict than GCC, so it would be great to have an Clang 10 build.

[kunaltyagi]

Let's have a clang CI in that case.

What would be a good way to run the clang CI?

• Before/After Ubuntu CI (since it's ubuntu, but more restrictive): increases CI build time, but saves 2 or 1 slot (depending on before/after)
• After macOS CI (because it's a better clang): macOS CI finish the fastest. saves slot and time
• With Ubuntu CI (a simple addition in the CI matrix): consumes 1 more slot and doesn't save time in case of compilation failure

[SunBlack]

I would add it behind macOS, so you have one line with GCC (Ubuntu), one with Clang (macOS/Ubuntu), MSVC (Windows)