rust: pin unicode-segmentation crate to 1.12.0

unicode-segmentation (used by rustyline) was updated from 1.12.0 to
1.13.1 earlier and requires a newer version of Rust. Pin to 1.12.0 which
works with Rust 1.75.0.

rust/Cargo.lock.in

@@ -1665,6 +1665,7 @@ dependencies = [
  "serde",
  "serde_json",
  "thiserror 1.0.69",
+ "unicode-segmentation",
 ]
 
 [[package]]

rust/suricatasc/Cargo.toml.in

@@ -25,6 +25,7 @@ serde_json = { version = "1.0.140", default-features = false, features = ["prese
 
 # Pinned back to support Rust 1.75.0. Not used directly by us, but by rustyline.
 home = { version = "=0.5.9" }
+unicode-segmentation = { version = "=1.12.0" }
 
 # Pinned back to support Rust 1.75.0. Not used directly by us, but by serde_json.
 indexmap = { version = "=2.11.4" }