cmake: search capnproto in package mode only

CMake does not provide a `FindCapnProto.cmake` module and never will,
because CapnProto already ships CMake package configuration files.
Make sure to skip the search for the CMake module and avoid the
confusing "By not providing ..." error message if CapnProto is not
installed.

Author: purpleKarrot

CMakeLists.txt

@@ -13,7 +13,7 @@ endif()
 include("cmake/compat_find.cmake")
 
 find_package(Threads REQUIRED)
-find_package(CapnProto 0.7 REQUIRED)
+find_package(CapnProto 0.7 REQUIRED NO_MODULE)
 
 # Check for list-of-pointers memory access bug from Nov 2022
 # https://nvd.nist.gov/vuln/detail/CVE-2022-46149