On OBS I ran into:
...
binaries-testsuite.openSUSE_Factory.x86_64/gdb-testresults/gdb-x86_64-suse-linux-m64.sum:
  ...
[Wed Oct 27 20:19:51 2021] (8476/8476): started http server on IPv4 IPv6 port=8000^M
[Wed Oct 27 20:19:51 2021] (8476/8476): search concurrency 8^M
[Wed Oct 27 20:19:51 2021] (8476/8476): rescan time 300^M
[Wed Oct 27 20:19:51 2021] (8476/8476): fdcache fds 144^M
[Wed Oct 27 20:19:51 2021] (8476/8476): fdcache mbs 2881^M
[Wed Oct 27 20:19:51 2021] (8476/8476): fdcache prefetch 64^M
[Wed Oct 27 20:19:51 2021] (8476/8476): fdcache tmpdir /tmp^M
[Wed Oct 27 20:19:51 2021] (8476/8476): fdcache tmpdir min% 25^M
[Wed Oct 27 20:19:51 2021] (8476/8476): groom time 86400^M
builtin_spawn /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/../../gdb/gdb -nw -nx -data-directory /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/../data-directory -iex set height 0 -iex set width 0 -iex set build-id-verbose 0^M
GNU gdb (GDB; home:tomdevries:branches:devel:gcc-gdb-gdb-11-1-update) 11.1^M
Copyright (C) 2021 Free Software Foundation, Inc.^M
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>^M
This is free software: you are free to change and redistribute it.^M
There is NO WARRANTY, to the extent permitted by law.^M
Type "show copying" and "show warranty" for details.^M
This GDB was configured as "x86_64-suse-linux".^M
Type "show configuration" for configuration details.^M
For bug reporting instructions, please see:^M
<http://bugs.opensuse.org/>.^M
Find the GDB manual and other documentation resources online at:^M
    <http://www.gnu.org/software/gdb/documentation/>.^M
^M
For help, type "help".^M
Type "apropos word" to search for commands related to "word".^M
(gdb) set height 0^M
(gdb) set width 0^M
(gdb) set build-id-verbose 0^M
(gdb) dir^M
Reinitialize source path to empty? (y or n) y^M
Source directories searched: $cdir:$cwd^M
(gdb) dir /home/abuild/rpmbuild/BUILD/gdb-11.1/gdb/testsuite/gdb.debuginfod^M
Source directories searched: /home/abuild/rpmbuild/BUILD/gdb-11.1/gdb/testsuite/gdb.debuginfod:$cdir:$cwd^M
(gdb) kill^M
The program is not being run.^M
(gdb) file /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/outputs/gdb.debuginfod/fetch_src_and_symbols/fetch_src_and_symbols^M
Reading symbols from /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/outputs/gdb.debuginfod/fetch_src_and_symbols/fetch_src_and_symbols...^M
(No debugging symbols found in /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/outputs/gdb.debuginfod/fetch_src_and_symbols/fetch_src_and_symbols)^M
(gdb) set substitute-path /home/abuild/rpmbuild/BUILD/gdb-11.1/build-x86_64-suse-linux/gdb/testsuite.unix.-m64/outputs/gdb.debuginfod/fetch_src_and_symbols /dev/null^M
(gdb) PASS: gdb.debuginfod/fetch_src_and_symbols.exp: local_url: set substitute-path
br main^M
Breakpoint 1 at 0x112d^M
(gdb) FAIL: gdb.debuginfod/fetch_src_and_symbols.exp: local_url: br main
l^M
No symbol table is loaded.  Use the "file" command.^M
(gdb) FAIL: gdb.debuginfod/fetch_src_and_symbols.exp: local_url: l
...

I'll try to reproduce this.

FWIW, the test-case is not too forthcoming with reasons why no symbols are read.

F.i., it could be nice to print the env var from within gdb.

Or, perhaps a status command, like "(maint) info debuginfod" to print current status of the client.