Fix a deprecation warning with newer Perl that breaks some tests.

--- a/tp/Texinfo/Parser.pm
+++ b/tp/Texinfo/Parser.pm
@@ -5438,12 +5438,12 @@
     }
   } elsif ($command eq 'clickstyle') {
     # REMACRO
-    if ($line =~ /^\s+@([[:alnum:]][[:alnum:]\-]*)({})?\s*/) {
+    if ($line =~ /^\s+@([[:alnum:]][[:alnum:]\-]*)(\{})?\s*/) {
       $args = ['@'.$1];
       $self->{'clickstyle'} = $1
         unless(_ignore_global_commands($self));
       $remaining = $line;
-      $remaining =~ s/^\s+@([[:alnum:]][[:alnum:]\-]*)({})?\s*(\@(c|comment)((\@|\s+).*)?)?//;
+      $remaining =~ s/^\s+@([[:alnum:]][[:alnum:]\-]*)(\{})?\s*(\@(c|comment)((\@|\s+).*)?)?//;
       $has_comment = 1 if (defined($4));
     } else {
       $self->line_error (sprintf($self->__(
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<div class='path'>path: <a href='/guix/log/?id=756f5411a98e250653dd76abf78e4f48b4d408d5'>root</a>/<a href='/guix/log/tests?id=756f5411a98e250653dd76abf78e4f48b4d408d5'>tests</a>/<a href='/guix/log/tests/pack.scm?id=756f5411a98e250653dd76abf78e4f48b4d408d5'>pack.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/tests/pack.scm?id=756f5411a98e250653dd76abf78e4f48b4d408d5&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2021-07-18 02:02:34 -0400'>2021-07-18</span></td><td><a href='/guix/commit/tests/pack.scm?id=aeded14b8342c1e72afd014a1bc121770f8c3a1c'>pack: Allow embedding custom control files in deb packs.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-06-29 14:53:21 -0400'>2021-06-29</span></td><td><a href='/guix/commit/tests/pack.scm?id=82daab42811a2e3c7684ebdf12af75ff0fa67b99'>pack: Add support for the deb format.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>
<tr><td><span title='2021-06-29 14:53:21 -0400'>2021-06-29</span></td><td><a href='/guix/commit/tests/pack.scm?id=8108c266dc2fbc70602b2aa5c6887bf17bed16e8'>tests: pack: Fix compressor extension.</a><span class='msg-avail'>...</span></td><td>Maxim Cournoyer</td></tr>