Replace __attribute__((constructor)) with C++ constructor.

The use of __attribute__((constructor)) made the previous commit fail to build in MSVC.

PiperOrigin-RevId: 474891117
Change-Id: I86a71bb8f3226ee49a8b5e8c07adc613623042b3

.github/workflows/build.yml

@@ -17,6 +17,7 @@ on:
 jobs:
   mujoco:
     strategy:
+      fail-fast: false
       matrix:
         include:
           - os: ubuntu-22.04

test/engine/engine_plugin_test.cc

@@ -31,7 +31,6 @@
 
 namespace mujoco {
 namespace {
-using PluginTest = MujocoTest;
 using ::testing::HasSubstr;
 using ::testing::NotNull;
 
@@ -271,7 +270,10 @@ int RegisterActuatorPlugin() {
   return mjp_registerPlugin(&plugin);
 }
 
-__attribute__((constructor)) void RegisterAllPlugins() {
+class PluginTest : public MujocoTest {
+ public:
+  // register all plugins
+  PluginTest() : MujocoTest() {
     RegisterSensorPlugin();
 
     for (int i = 1; i <= kNumFakePlugins; ++i) {
@@ -284,6 +286,7 @@ __attribute__((constructor)) void RegisterAllPlugins() {
 
     RegisterActuatorPlugin();
   }
+};
 
 constexpr char xml[] = R"(
 <mujoco>