ci: prepare: Install GDB

The RPM build tools in Fedora 41 apparently require `gdb` but don't
declare that:

> find-debuginfo: starting
> Extracting debug info from 1 files
> gdb-add-index: Failed to find a useable GDB binary

ci/prepare.sh

@@ -4,6 +4,7 @@ dnf install -y \
 	--setopt install_weak_deps=0 \
 	cargo \
 	cargo-rpm-macros \
+	gdb \
 	make \
 	openssh-clients \
 	openssl-devel \