Plugins: Add missing asserts for Plugin Errors field (#51702)

* make sure to check plugin errors

* remove unused test

pkg/plugins/manager/loader/loader_test.go

@@ -531,8 +531,8 @@ func TestLoader_Load_MultiplePlugins(t *testing.T) {
 					},
 				},
 				pluginErrors: map[string]*plugins.Error{
-					"test": {
-						PluginID:  "test",
+					"test-panel": {
+						PluginID:  "test-panel",
 						ErrorCode: "signatureMissing",
 					},
 				},
@@ -556,6 +556,11 @@ func TestLoader_Load_MultiplePlugins(t *testing.T) {
 				if !cmp.Equal(got, tt.want, compareOpts) {
 					t.Fatalf("Result mismatch (-want +got):\n%s", cmp.Diff(got, tt.want, compareOpts))
 				}
+				pluginErrs := l.PluginErrors()
+				require.Equal(t, len(tt.pluginErrors), len(pluginErrs))
+				for _, pluginErr := range pluginErrs {
+					require.Equal(t, tt.pluginErrors[pluginErr.PluginID], pluginErr)
+				}
 			})
 		}
 	})