languages: Fix Markdown list items are automatically indented erroneously (#44381)

Closes #44223

Regressed in https://github.com/zed-industries/zed/pull/40794 in attempt
to fix https://github.com/zed-industries/zed/issues/40757. This PR
handles both cases and add more tests around it.

Bug is only in Nightly.

Release Notes:

- N/A

crates/languages/src/markdown/config.toml

@@ -24,5 +24,5 @@ rewrap_prefixes = [
 auto_indent_on_paste = false
 auto_indent_using_last_non_empty_line = false
 tab_size = 2
-decrease_indent_pattern = "^\\s*$"
+decrease_indent_pattern = "^.*$"
 prettier_parser_name = "markdown"

crates/languages/src/markdown/indents.scm

@@ -1,3 +1 @@
 (list (list_item) @indent)
-
-(list_item (list) @indent)