fix: auth with no docker config

Don't error when looking up auth if no docker configuration file exists,
instead treat it as no authentication was provided.

Fixes #2767

docker_auth.go

@@ -165,6 +165,10 @@ func configFileKey() (string, error) {
 func getDockerAuthConfigs() (map[string]registry.AuthConfig, error) {
 	cfg, err := getDockerConfig()
 	if err != nil {
+		if errors.Is(err, os.ErrNotExist) {
+			return map[string]registry.AuthConfig{}, nil
+		}
+
 		return nil, err
 	}
 

docker_auth_test.go

@@ -414,4 +414,15 @@ func Test_getDockerAuthConfigs(t *testing.T) {
 		}
 		require.Equal(t, expected, got)
 	})
+
+	t.Run("file-not-found", func(t *testing.T) {
+		t.Setenv("DOCKER_CONFIG", "")
+		tmp := t.TempDir()
+		t.Setenv("HOME", tmp)
+		t.Setenv("USERPROFILE", tmp) // Windows
+
+		cfg, err := getDockerAuthConfigs()
+		require.NoError(t, err)
+		require.Empty(t, cfg)
+	})
 }