Make the divider rule color more muted (#19255)

I've been a bit annoyed by the hover divider rule being extremely bright
compared to other divider rules in the UI. This PR updates their color
to use the regular border color from the current theme instead of the
muted (but still pretty bright) text color.

Apologies for the unsolicited PR (and please feel free to close if it
goes against some other plans / designs you already have in place :).

#### Example screenshot before:
<img width="302" alt="Screenshot 2024-10-15 at 23 29 18"
src="https://github.com/user-attachments/assets/7ea22808-8135-4a46-9457-e670225aebaa">

#### Example screenshot after:
<img width="312" alt="Screenshot 2024-10-15 at 23 28 16"
src="https://github.com/user-attachments/assets/63ac0d02-ae6d-4962-84a2-1fdb95519b15">

***

Release Notes:

- Make the divider rule in LSP hovers more muted

crates/editor/src/hover_popover.rs

@@ -525,7 +525,7 @@ async fn parse_blocks(
                     font_family: Some(buffer_font_family),
                     ..Default::default()
                 },
-                rule_color: Color::Muted.color(cx),
+                rule_color: cx.theme().colors().border,
                 block_quote_border_color: Color::Muted.color(cx),
                 block_quote: TextStyleRefinement {
                     color: Some(Color::Muted.color(cx)),