gh: insert empty helper when using credential helper (#7347)

Resets previous helpers so the only one being used is the `gh` cli

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/programs/gh.nix

@@ -193,7 +193,10 @@ in
         map (
           host:
           lib.nameValuePair host {
-            helper = "${cfg.package}/bin/gh auth git-credential";
+            helper = [
+              ""
+              "${cfg.package}/bin/gh auth git-credential"
+            ];
           }
         ) cfg.gitCredentialHelper.hosts
       )

tests/modules/programs/gh/credential-helper.git.conf

@@ -1,7 +1,9 @@
 [credential "https://github.com"]
+	helper = ""
 	helper = "@gh@/bin/gh auth git-credential"
 
 [credential "https://github.example.com"]
+	helper = ""
 	helper = "@gh@/bin/gh auth git-credential"
 
 [gpg]