Add debug message if we could not get a guard

Issue: https://progress.opensuse.org/issues/164898

lib/OpenQA/Task/Git/Clone.pm

@@ -6,6 +6,7 @@ use Mojo::Base 'Mojolicious::Plugin', -signatures;
 use Mojo::Util 'trim';
 
 use Mojo::File;
+use OpenQA::Log qw(log_debug);
 use Time::Seconds 'ONE_HOUR';
 
 sub register ($self, $app, @) {
@@ -30,9 +31,14 @@ sub _git_clone_all ($job, $clones) {
     # Prevent multiple git_clone tasks for the same path to run in parallel
     my @guards;
     for my $path (sort keys %$clones) {
+        my $guard_name = "git_clone_${path}_task";
         $path = Mojo::File->new($path)->realpath if -e $path;    # resolve symlinks
-        my $guard = $app->minion->guard("git_clone_${path}_task", 2 * ONE_HOUR);
-        return $job->retry($retry_delay) unless $guard;
+        my $guard = $app->minion->guard($guard_name, 2 * ONE_HOUR);
+        unless ($guard) {
+            log_debug("Could not get guard for '$guard_name', retrying in $retry_delay->{delay}s")
+              ;    # uncoverable statement
+            return $job->retry($retry_delay);    # uncoverable statement
+        }
         push @guards, $guard;
     }