Fix ghostel-test-package-version failure with stale .elc

locate-library prefers .elc over .el, so after a byte-compile
(e.g. from make lint), the test reads bytecode instead of source
and lm-header can't find the Version header.  Use
(locate-library "ghostel.el" t) to explicitly find the source file.

Also update test to use renamed ghostel--suppress-interfering-modes.

Author: dakra

ghostel.el

@@ -447,7 +447,7 @@ matches the GitHub release tag even when MELPA rewrites the
 version to a date-based string."
   (require 'lisp-mnt nil t)
   (when (fboundp 'lm-header)
-    (let ((lib (or load-file-name (locate-library "ghostel"))))
+    (let ((lib (or load-file-name (locate-library "ghostel.el" t))))
       (when lib
         (with-temp-buffer
           (insert-file-contents lib nil 0 1024)

test/ghostel-test.el

@@ -1136,7 +1136,7 @@ cell, so the visual line width must equal the terminal column count."
           (let ((global-hl-line-mode t))
             (should global-hl-line-mode)
             ;; Suppress should opt this buffer out
-            (ghostel--suppress-hl-line-mode)
+            (ghostel--suppress-interfering-modes)
             (should ghostel--saved-hl-line-mode)
             ;; Buffer-local global-hl-line-mode must be nil — this is the
             ;; mechanism that prevents global-hl-line-highlight (on