Signs cannot be customized

## Information

**VIM version**
NVIM v0.9.5

Operating System:
Fedora 40
## What went wrong

On `master` branch, the following customizations have no effect:
https://github.com/dense-analysis/ale?tab=readme-ov-file#how-can-i-customise-signs
The signs are always `I`, `W`, and `E`. Also, `let g:ale_sign_column_always = 1` doesn't keep the column always visible.

On tagged release `3.3.0` there is no issue.

## Reproducing the bug

1. Install `shellcheck`
2. Open `test.sh` file with contents:
```
#!/bin/bash

echo $a
```
3. Run nvim command `let g:ale_sign_warning = '--'`
4. The last line's column warning sign is still `W`

### :ALEInfo

Current Filetype: sh
Available Linters: ['bashate', 'cspell', 'language_server', 'shell', 'shellcheck']
Enabled Linters: ['bashate', 'cspell', 'language_server', 'shell', 'shellcheck']
Ignored Linters: []
Suggested Fixers:
'remove_trailing_lines' - Remove all blank lines at the end of a file.
'shfmt' - Fix sh files with shfmt.
'trim_whitespace' - Remove all trailing whitespace characters at the end of every line.

Linter Variables:
" Press Space to read :help for a setting
let g:ale_sh_bashate_executable = 'bashate'
let g:ale_sh_bashate_options = ''
let g:ale_sh_language_server_executable = 'bash-language-server'
let g:ale_sh_language_server_use_global = 0
let g:ale_sh_shell_default_shell = 'bash'
let g:ale_sh_shellcheck_change_directory = 1
let g:ale_sh_shellcheck_dialect = 'auto'
let g:ale_sh_shellcheck_exclusions = ''
let g:ale_sh_shellcheck_executable = 'shellcheck'
let g:ale_sh_shellcheck_options = ''

Global Variables:
" Press Space to read :help for a setting
let g:ale_cache_executable_check_failures = v:null
let g:ale_change_sign_column_color = v:null
let g:ale_command_wrapper = ''
let g:ale_completion_delay = v:null
let g:ale_completion_enabled = 0
let g:ale_completion_max_suggestions = v:null
let g:ale_disable_lsp = 'auto'
let g:ale_echo_cursor = 1
let g:ale_echo_msg_error_str = 'Error'
let g:ale_echo_msg_format = '%code: %%s'
let g:ale_echo_msg_info_str = 'Info'
let g:ale_echo_msg_warning_str = 'Warning'
let g:ale_enabled = 1
let g:ale_fix_on_save = 0
let g:ale_fixers = {'sh': ['shfmt'], '*': ['remove_trailing_lines', 'trim_whitespace'], 'python': ['black']}
let g:ale_history_enabled = 1
let g:ale_info_default_mode = 'preview'
let g:ale_history_log_output = 1
let g:ale_keep_list_window_open = 0
let g:ale_lint_delay = 200
let g:ale_lint_on_enter = 1
let g:ale_lint_on_filetype_changed = 1
let g:ale_lint_on_insert_leave = 1
let g:ale_lint_on_save = 1
let g:ale_lint_on_text_changed = 'normal'
let g:ale_linter_aliases = {}
let g:ale_linters = {'perl': ['perl'], 'json': ['jq']}
let g:ale_linters_explicit = 0
let g:ale_linters_ignore = {}
let g:ale_list_vertical = 0
let g:ale_list_window_size = 10
let g:ale_loclist_msg_format = '%code: %%s'
let g:ale_max_buffer_history_size = 20
let g:ale_max_signs = v:null
let g:ale_maximum_file_size = v:null
let g:ale_open_list = 0
let g:ale_pattern_options = v:null
let g:ale_pattern_options_enabled = v:null
let g:ale_root = {}
let g:ale_set_balloons = 0
let g:ale_set_highlights = 1
let g:ale_set_loclist = 1
let g:ale_set_quickfix = 0
let g:ale_set_signs = 1
let g:ale_sign_column_always = v:null
let g:ale_sign_error = v:null
let g:ale_sign_info = v:null
let g:ale_sign_offset = v:null
let g:ale_sign_style_error = v:null
let g:ale_sign_style_warning = v:null
let g:ale_sign_warning = '--'
let g:ale_sign_highlight_linenrs = v:null
let g:ale_type_map = {}
let g:ale_use_neovim_diagnostics_api = 1
let g:ale_use_global_executables = v:null
let g:ale_virtualtext_cursor = 'all'
let g:ale_warn_about_trailing_blank_lines = 1
let g:ale_warn_about_trailing_whitespace = 1

LSP Error Messages:

(Errors for language_server)
Failed to find project root, language server won't start.
Failed to find project root, language server won't start.
Command History:

(executable check - failure) bashate
(executable check - failure) cspell
(executable check - success) bash
(finished - exit code 0) ['/usr/bin/bash', '-c', 'bash -n ''/tmp/nvim.user/W4Z41K/1/dupa.sh''']

<<>>

(executable check - success) shellcheck
(finished - exit code 0) ['/usr/bin/bash', '-c', 'cd ''/tmp/_opt/_'' && ''shellcheck'' --version']

<<>>
ShellCheck - shell script analysis tool
version: 0.9.0
license: GNU General Public License, version 3
website: https://www.shellcheck.net
<<>>

(finished - exit code 0) ['/usr/bin/bash', '-c', 'cd ''/tmp/_opt/_'' && ''shellcheck'' -s bash -x -f json1 - < ''/tmp/nvim.user/W4Z41K/2/dupa.sh''']

<<>>
{"comments":[]}
<<>>

(executable check - failure) bashate
(executable check - failure) cspell
(finished - exit code 0) ['/usr/bin/bash', '-c', 'bash -n ''/tmp/nvim.user/W4Z41K/3/dupa.sh''']

<<>>

(finished - exit code 1) ['/usr/bin/bash', '-c', 'cd ''/tmp/_opt/_'' && ''shellcheck'' -s bash -x -f json1 - < ''/tmp/nvim.user/W4Z41K/4/dupa.sh''']

<<>>
{"comments":[{"file":"-","line":3,"endLine":3,"column":6,"endColumn":8,"level":"warning","code":2154,"message":"a is referenced but not assigned.","fix":null},{"file":"-","line":3,"endLine":3,"column":6,"endColumn":8,"level":"info","code":2086,"message":"Double quote to prevent globbing and word splitting.","fix":{"replacements":[{"column":6,"endColumn":6,"endLine":3,"insertionPoint":"afterEnd","line":3,"precedence":7,"replacement":"\""},{"column":8,"endColumn":8,"endLine":3,"insertionPoint":"beforeStart","line":3,"precedence":7,"replacement":"\""}]}}]}
<<>>