Force older gdb version in CI due to index create regression in 15.1

gdb 15.1 causes our "rpmbuild debuginfo gdb index included" to fail
because no index is created. Reported to Fedora bugzilla:
https://bugzilla.redhat.com/show_bug.cgi?id=2310156

Related: rpm-software-management#3278

tests/Dockerfile.fedora

@@ -46,7 +46,7 @@ RUN dnf -y install \
   tar unzip gzip bzip2 cpio xz p7zip-plugins \
   pkgconfig \
   /usr/bin/systemd-sysusers \
-  /usr/bin/gdb-add-index \
+  gdb-headless-14.2 \
   dwz \
   fsverity-utils fsverity-utils-devel \
   pandoc \