## What is this PR for?
Fix detection of elixir `credo` linter.
`vim.fn.executable("credo") == 0` will never succeed because `credo` is
not binary/executable. It is a `mix` package and only available via `mix
credo` command.
Instead, the plugins(both `none-ls` and `nvim-lint`) will check for the
presence of the `.credo.exs` file.
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## Does this PR fix an existing issue?
Fixes#3808
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## Checklist
- [x] Both linters display credo warnings if `credo` is installed and
the `.credo.exs` config exists in a project.
- [x] There are no errors if the `.credo.exs` file does not exist in the
project.
- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.
## What is this PR for?
add missing elixir lspconfig
## Does this PR fix an existing issue?
lspconfig is missing for elixir and since mason was removed in
f8268faa7c,
elixirls is no longer automatically installed.
## Checklist
- [x] I've read the
[CONTRIBUTING](https://github.com/LazyVim/LazyVim/blob/main/CONTRIBUTING.md)
guidelines.
