build: Do not use lcov-inject first argument as target directory

All arguments are files to modify.

doc/lcov-inject

@@ -24,7 +24,7 @@ use warnings;
 use Cwd;
 use Devel::Cover::DB;
 
-my $dir = $ARGV[0] // 'scripts';
+my $dir = 'scripts';
 my $cwd = cwd();
 
 chdir $dir or die "cannot switch to $dir\n";