Avoid "already compiled" warning in erc-compat

* lisp/erc/erc-compat.el (erc-compat--29-auth-source-pass-search):
Don't `byte-compile' sub-29 secrets wrapper.  This was especially
noisy in tests.  Ditch closed-over vars via HOF instead of suppressing
because compiling emits "unused lexical" warning on Emacs 27.

lisp/erc/erc-compat.el

@@ -261,7 +261,7 @@ If START or END is negative, it counts from the end."
             (when-let* ((s (plist-get e :secret))
                         (v (auth-source--obfuscate s)))
               (setf (plist-get e :secret)
-                    (byte-compile (lambda () (auth-source--deobfuscate v)))))
+                    (apply-partially #'auth-source--deobfuscate v)))
             (push e out)))
       rv)))