Remove fake credentials from test file: use Guid.NewGuid() for test passwords

Co-authored-by: marekzmyslowski <1062877+marekzmyslowski@users.noreply.github.com>

Author: Copilot

src/shared/Core.Tests/Interop/Posix/GnuPassCredentialStoreTests.cs

@@ -99,7 +99,7 @@ public void GnuPassCredentialStore_ReadWriteDelete_GpgIdInSubdirectory()
             string uniqueGuid = Guid.NewGuid().ToString("N");
             string service = $"https://example.com/{uniqueGuid}";
             const string userName = "john.doe";
-            const string password = "letmein123"; // [SuppressMessage("Microsoft.Security", "CS001:SecretInline", Justification="Fake credential")]
+            string password = Guid.NewGuid().ToString("N");
 
             try
             {
@@ -151,7 +151,7 @@ public void GnuPassCredentialStore_WriteCredential_MultipleGpgIds_UsesNearestGpg
 
             string service = $"https://example.com/{Guid.NewGuid():N}";
             const string userName = "john.doe";
-            const string password = "letmein123"; // [SuppressMessage("Microsoft.Security", "CS001:SecretInline", Justification="Fake credential")]
+            string password = Guid.NewGuid().ToString("N");
 
             try
             {