Core/Scripting: Fix acquiring of references between script swaps

* Delay unloading of shared libraries to the next update tick
  to prevent crashes in the destructor of the last referenced
  script instance.
* Closes #17557

(cherry picked from commit 445746c402)

src/server/game/Scripting/ScriptMgr.cpp

@@ -987,7 +987,7 @@ void ScriptMgr::Initialize()
     FillSpellSummary();
 
     // Load core scripts
-    SetScriptContext("___static___");
+    SetScriptContext(GetNameOfStaticContext());
 
     // SmartAI
     AddSC_SmartScripts();
@@ -1042,6 +1042,12 @@ void ScriptMgr::SwapScriptContext(bool initialize)
     _currentContext.clear();
 }
 
+std::string const& ScriptMgr::GetNameOfStaticContext()
+{
+    static std::string const name = "___static___";
+    return name;
+}
+
 void ScriptMgr::ReleaseScriptContext(std::string const& context)
 {
     sScriptRegistryCompositum->ReleaseContext(context);