lang/csharp: updated bindings

Specifically:
- `t-a` -> `t-s` ("unit test all" is now "unit test buffer")
- `t-r` -> `t-l` ("unit test ?" is now "unit test last")
- `t-s` is the same (couldn't think of anything better)

modules/lang/csharp/config.el

@@ -52,6 +52,9 @@
           "ti" #'omnisharp-current-type-information
           "td" #'omnisharp-current-type-documentation)
         (:prefix "t"
+          "s" #'omnisharp-unit-test-at-point
+          "l" #'omnisharp-unit-test-last
+          "b" #'omnisharp-unit-test-buffer)))
 
 
 (when (featurep! +unity)