Manifest contains entries without a .rock

[mrcjkb]

Some tree-sitter parser packages contain only queries don't have a source,
and luarocks pack doesn't create a .rock file for them. But the generated manifest contains entries, leading to installation failures such as

Error: Could not fetch rock file: Error fetching file: Failed downloading https://nvim-neorocks.github.io/rocks-binaries/tree-sitter-ecma-0.0.1-1.all.rock - failed downloading https://nvim-neorocks.github.io/rocks-binaries/tree-sitter-ecma-0.0.1-1.all.rock

This is a potential luarocks bug, but we need to find a workaround here.

Strangely, there are .rocks in rocks-binaries-dev.