Couldn't enable `opam-switch-mode` in Coq projects

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- [X] The issue can be reproduced on the **latest** available commit of Doom.

- [X] The issue can be reproduced on a stable release of Emacs, such as 27, 28, or 29. *(Unstable versions end in .50, .60, or .9x)*

### Expected behavior

When I enable `opam-switch-mode` in a Coq project, there shouldn't be any errors.

### Current behavior

I got `opam-switch-set-switch: Symbol’s function definition is void: tuareg-opam-current-compiler`.

This bug seems to have been introduced after #7806, which calls this function when first loading `opam-switch-mode`, regardless of whether the `tuareg` package (the OCaml mode) is loaded.

While opam is commonly used for OCaml projects, it is also used in some Coq projects.

### Steps to reproduce

1. Enable `coq` module `config.el`
2. Open a `.v` file in a Coq project
3. `M-x opam-switch-mode`

### System Information

https://pastebin.com/fEe1nJcK