fix(blink): enable Neovim native mapping with <Tab> (#5617)

## Description
Another blink fix unfortunately. 

I noticed that native Neovim `<Tab>` completion didn't work after the
breaking commit.

I checked the commit and noticed it had a boolean `enabled` field, so I
thought maybe that would disable the blink cmdline since we already have
`sources = {}`, but it didn't work. Looking through the commit, I
stumbled upon this piece of
[code](93215d8034 (diff-f313d6f0270f6fed848f1cb7e62c82d3cfaf9b6c7e0072266908eeaf202f11d5R66-R68))
and it seems that it's only checked for applying the blink cmdline
mappings.

So, it seems both `enabled = false` (for Neovim native cmdline mapping)
and `sources = {}` are needed to have default Neovim cmdline experience.

PS: Apparently I don't know how to link from the commit the necessary
part of the commit, so I'm just referencing here the part of the code
[directly in the
file](426a605518/lua/blink/cmp/keymap/init.lua (L66-L70)).
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## Related Issue(s)
None
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## Screenshots

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## Checklist

- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.

lua/lazyvim/plugins/extras/coding/blink.lua

@@ -82,6 +82,7 @@ return {
       },
 
       cmdline = {
+        enabled = false,
         sources = {},
       },