ci: Bump LLVM version we use to 16

Development on LLVM 16 has started and version 15 is no longer available
in the repository we install it from. Bump the version we use
accordingly.

Signed-off-by: Daniel Müller <deso@posteo.net>

.github/actions/build-selftests/build_selftests.sh

@@ -8,7 +8,7 @@ source ${THISDIR}/helpers.sh
 
 foldable start prepare_selftests "Building selftests"
 
-LLVM_VER=15
+LLVM_VER=16
 LIBBPF_PATH="${REPO_ROOT}"
 
 PREPARE_SELFTESTS_SCRIPT=${THISDIR}/prepare_selftests-${KERNEL}.sh