lsp-bash: only take into account buffer-local sh-shell

[fredericgiquel]

Recent changes (#4620) make lsp-bash eligible for all buffers if Emacs is launch from a bash shell. It's because sh-shell is a global variable and its value is set to the shell used to launch Emacs (and there is no more major-mode check in lsp-bash-check-sh-shell).

This can lead to choose the wrong server (depending on priorities). For example, if I open a typescript file, I can observe the following logs:

Command "semgrep lsp" is not present on the path.
Command "deno lsp" is not present on the path.
Command "typescript-language-server --stdio" is present on the path.
Command "bash-language-server start" is present on the path.
Found the following clients for /home/fred/Projets/test/test.ts: (server-id ts-ls, priority -2), (server-id bash-ls, priority -1)
The following clients were selected based on priority: (server-id bash-ls, priority -1)

To fix the problem, we can reintroduce major-mode check or only take into account buffer-local sh-shell (as proposed by this PR). Feel free to choose the solution you prefer.

[jcs090218]

Thank you!