Revert "Temporary downgrade kernel to 6.7 for integration tests"

The used kernel build is not installable anymore.

This reverts commit ce24963022.

integration/upstream-tests/test.sh

@@ -10,15 +10,6 @@ pushd "$WORKDIR"
 # shellcheck disable=SC2064
 trap "chmod -R o+rX $TMT_TEST_DATA" EXIT
 
-if [[ "${TMT_REBOOT_COUNT:?}" -eq 0 ]]; then
-    # Temporary workaround for a borked 6.8 kernel
-    koji download-build --arch=x86_64 kernel-6.7.0-68.fc40
-    rm -f ./kernel-*debug*.rpm
-    dnf -y install ./kernel*.rpm
-    grubby --set-default /boot/vmlinuz-6.7.0-68.fc40.x86_64
-    tmt-reboot
-fi
-
 # Switch SELinux to permissive, since the tests don't set proper contexts
 setenforce 0