[Bug] Rocks sync should not invoke luarocks [install|uninstall|update] concurrently

[mrcjkb]

This leads to partial uninstalls

To reproduce:

• Install a bunch of plugins.
• Remove all plugins from rocks.toml.
• Run Rocks sync.
• Wait for it to finish.
• Run Rocks sync again.

Expected behaviour:

• Progress message says everything is in sync.

Actual behaviour:

• An error message is displayed, saying the rockspec of a previously pruned plugin can\t be found.

This appears to be because of an incomplete uninstall.

Excample:

Error executing vim.schedule lua callback: ...pack/myNeovimPackages/start/rocks.nvim/lua/nio/tasks.lua:95: Async task failed without callback: The
coroutine failed with this message:
...ck/myNeovimPackages/start/rocks.nvim/lua/nio/control.lua:107:
Error: Could not load rockspec file /home/mrcjk/.local/share/nvimrocks/rocks/lib/luarocks/rocks-5.1/haskell-snippets.nvim/1.4.2-1/haskell-snippets.
nvim-1.4.2-1.rockspec (/home/mrcjk/.local/share/nvimrocks/rocks/lib/luarocks/rocks-5.1/haskell-snippets.nvim/1.4.2-1/haskell-snippets.nvim-1.4.2-1.
rockspec: No such file or directory)

stack traceback:
        [C]: in function 'error'
        ...ck/myNeovimPackages/start/rocks.nvim/lua/nio/control.lua:107: in function 'wait'
        ...ck/myNeovimPackages/start/rocks.nvim/lua/rocks/state.lua:112: in function 'rock_dependencies'
        ...NeovimPackages/start/rocks.nvim/lua/rocks/operations.lua:275: in function <...NeovimPackages/start/rocks.nvim/lua/rocks/operations.lua:1
54>
stack traceback:
        [C]: in function 'error'
        ...pack/myNeovimPackages/start/rocks.nvim/lua/nio/tasks.lua:95: in function 'close_task'
        ...pack/myNeovimPackages/start/rocks.nvim/lua/nio/tasks.lua:117: in function 'cb'
        ...pack/myNeovimPackages/start/rocks.nvim/lua/nio/tasks.lua:181: in function 'waiter'
        ...ck/myNeovimPackages/start/rocks.nvim/lua/nio/control.lua:81: in function 'wake'
        ...ck/myNeovimPackages/start/rocks.nvim/lua/nio/control.lua:99: in function 'set_error'
        ...ck/myNeovimPackages/start/rocks.nvim/lua/rocks/state.lua:106: in function ''
        vim/_editor.lua: in function <vim/_editor.lua:0>