Silence the following noisy warning:
```
CMake Warning at /usr/share/cmake/Modules/FindBoost.cmake:1384 (message):
New Boost version may have incorrect or missing dependencies and imported
targets
Call Stack (most recent call first):
/usr/share/cmake/Modules/FindBoost.cmake:1507 (_Boost_COMPONENT_DEPENDENCIES)
/usr/share/cmake/Modules/FindBoost.cmake:2118 (_Boost_MISSING_DEPENDENCIES)
cmake/modules/FindDEAL_II_BOOST.cmake:57 (find_package)
cmake/configure/configure_20_boost.cmake:36 (find_package)
/scratch/users/testsuite/build-3O4p1Svw/CMakeFiles/CMakeTmp/evaluate_expression.tmp:1 (feature_BOOST_find_external)
cmake/macros/macro_evaluate_expression.cmake:30 (include)
cmake/macros/macro_configure_feature.cmake:239 (evaluate_expression)
cmake/configure/configure_20_boost.cmake:170 (configure_feature)
cmake/macros/macro_verbose_include.cmake:19 (include)
CMakeLists.txt:130 (verbose_include)
```
# and https://lists.boost.org/Archives/boost/2019/02/245016.php
set(Boost_NO_BOOST_CMAKE ON)
+set(Boost_NO_WARN_NEW_VERSIONS TRUE)
if(DEAL_II_WITH_ZLIB)
find_package(Boost ${BOOST_VERSION_REQUIRED} COMPONENTS
iostreams serialization system thread
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