Avoid leaking repo.lock handle

The repo.lock file would be opened when installing a distribution,
but would never get closed. On windows this could manifest as an
error saying it can't delete repo.lock because the resource is
busy. This updates CURI.install to close the repo.lock file when
leaving the function.

src/core.c/CompUnit/Repository/Installation.rakumod

@@ -231,6 +231,7 @@ sub MAIN(*@, *%) {
         my @*MODULES;
         my $path   = self!writeable-path or die "No writeable path found, $.prefix not writeable";
         my $lock = $.prefix.add('repo.lock').open(:create, :w);
+        LEAVE $lock.close;
         $lock.lock;
 
         my $version = self!repository-version;