languages: Detect .bst files as YAML (#45015)

These files are used by the BuildStream build project:
https://buildstream.build/index.html


Release Notes:

- Added recognition for .bst files as yaml.

crates/languages/src/yaml/config.toml

@@ -1,6 +1,6 @@
 name = "YAML"
 grammar = "yaml"
-path_suffixes = ["yml", "yaml", "pixi.lock", "clang-format", "clangd"]
+path_suffixes = ["yml", "yaml", "pixi.lock", "clang-format", "clangd", "bst"]
 line_comments = ["# "]
 autoclose_before = ",]}"
 brackets = [