[libcxx][test] Require long_tests for eval.PR44847.pass.cp (#100722)

This takes 1m40s to run when testing picolib on qemu. This isn't the end
of the world but that's on an AArch64 server. So if someone felt the
need to mark this unsupported in the first place, it's likely much
slower on average hardware.

Author: DavidSpickett

libcxx/test/std/numerics/rand/rand.dist/rand.dist.bern/rand.dist.bern.bin/eval.PR44847.pass.cpp

@@ -18,8 +18,8 @@
 // Serializing/deserializing the state of the RNG requires iostreams
 // UNSUPPORTED: no-localization
 
-// This test appears to hang with picolibc & qemu.
-// UNSUPPORTED: LIBCXX-PICOLIBC-FIXME
+// Very slow when run in qemu.
+// REQUIRES: long_tests
 
 #include <random>
 #include <numeric>