chore(injections)!: update injection syntax to 0.9

Since 0.9, @lang syntax is still available as fallback but will soon be deprecated.
Because of that, new syntax should be adopted once 0.9 becomes the
baseline requirements for nvim-treesitter

- update health check
- update doc

queries/git_rebase/injections.scm

@@ -1,5 +1,6 @@
 ((operation
    (command) @_command
-   (message) @bash)
+   (message) @injection.content)
+(#set! injection.language "bash")
 (#any-of? @_command "exec" "x"))