FindBoost: Add support for Boost 1.86

Update the list of known versions.

Run the command

    cmake -DBOOST_DIR=/path/to/boost_1_86_0 \
      -P Utilities/Scripts/BoostScanDeps.cmake

to extract dependencies from the 1.86.0 source tree.
They are the same as 1.85's dependencies, so just update
the version check for warning about newer versions.

Fixes: #26433