Don't fall off the end of perl functions

This complies with the perlcritic policy
Subroutines::RequireFinalReturn, which is a severity 4 policy. Since we
only currently check at severity level 5, the policy is raised to that
level until we move to level 4 or lower, so that any new infringements
will be caught.

A small cosmetic piece of tidying of the pgperlcritic script is
included.

Mike Blackwell

Discussion: https://postgr.es/m/CAESHdJpfFm_9wQnQ3koY3c91FoRQsO-fh02za9R3OEMndOn84A@mail.gmail.com

src/tools/git_changelog

@@ -333,6 +333,7 @@ sub push_commit
 	push @{ $all_commits_by_branch{ $c->{'branch'} } }, $cc;
 	$cc->{'branch_position'}{ $c->{'branch'} } =
 	  -1 + @{ $all_commits_by_branch{ $c->{'branch'} } };
+	return;
 }
 
 sub hash_commit
@@ -355,6 +356,7 @@ sub parse_datetime
 sub output_str
 {
 	($oldest_first) ? ($output_line .= sprintf(shift, @_)) : printf(@_);
+	return;
 }
 
 sub output_details
@@ -395,6 +397,7 @@ sub output_details
 		}
 	}
 	output_str("\n");
+	return;
 }
 
 sub usage