style: satisfy prompt suffix checkdoc

Author: tninja

ai-code-prompt-mode.el

@@ -88,7 +88,7 @@ non-empty string or nil.  Provider errors abort the send."
         (cond
          ((null suffix) nil)
          ((not (stringp suffix))
-          (error "returned %S instead of a string or nil" suffix))
+          (error "Returned %S instead of a string or nil" suffix))
          ((string-empty-p suffix) nil)
          (t suffix)))
     (error

test/test_ai-code-prompt-mode.el

@@ -75,7 +75,7 @@
 (ert-deftest ai-code-test-prompt-suffix-provider-error-aborts-send ()
   "A failing suffix provider should stop the send operation."
   (let ((ai-code-prompt-suffix-functions
-         (list (lambda (_context) (error "broken provider"))))
+         (list (lambda (_context) (error "Broken provider"))))
         (ai-code-prompt-suffix nil)
         (ai-code-auto-test-type nil)
         (ai-code-auto-test-suffix nil)