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=088347300bb4d63c3fac50364f052525a91a5400'>root</a>/<a href='/guix/log/tests?id=088347300bb4d63c3fac50364f052525a91a5400'>tests</a>/<a href='/guix/log/tests/base32.scm?id=088347300bb4d63c3fac50364f052525a91a5400'>base32.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/base32.scm?id=088347300bb4d63c3fac50364f052525a91a5400&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2020-08-29 16:24:17 +0200'>2020-08-29</span></td><td><a href='/guix/commit/tests/base32.scm?id=d7965b58d25c9c7648ba5682223f32d759fdffda'>build: Remove references to the 'nix-hash' program.</a><span class='msg-avail'>...<span class='msg-tooltip'>* configure.ac: Remove check for 'nix-hash'.
* tests/base32.scm (%nix-hash, %have-nix-hash?): Remove.
("sha256 &amp; bytevector-&gt;nix-base32-string"): Remove test.
* build-aux/pre-inst-env.in: Do not set 'NIX_HASH' environment
variable.
</span></span></td><td>Ludovic Courtès</td></tr>