Suppress `-Wdeprecated-copy` on Clang 13

[Kojoley]

Clang 13 now also emits -Wdeprecated-copy when a copy assign operator is deleted. Since we need both actor to be an aggregate and to disallow assignment -- the only other way is to suppress the warning.

[Kojoley]

@djowel I've fixed the CI if that was blocking the merge.

[Flamefire]

Why not handle the warning? I failed to reproduce the warning with a simple example only deleting the assignment operator and found that is_pod still yields true when the default constructor is defaulted: https://godbolt.org/z/oaE8ndE3x

[Kojoley]

From [dcl.init.aggr] p1:

An aggregate is an array or a class ([class]) with

• no user-declared or inherited constructors ([class.ctor]),

From [diff.cpp17] p3:

Affected subclause: [dcl.init.aggr] Change: A class that has user-declared constructors is never an aggregate. Rationale: Remove potentially error-prone aggregate initialization which may apply notwithstanding the declared constructors of a class. Effect on original feature: Valid C++ 2017 code that aggregate-initializes a type with a user-declared constructor may be ill-formed or have different semantics in this revision of C++. For example:

struct A {              // not an aggregate; previously an aggregate
  A() = delete;
};

struct B {              // not an aggregate; previously an aggregate
  B() = default;
  int i = 0;
};

struct C {              // not an aggregate; previously an aggregate
  C(C&&) = default;
  int a, b;
};

A a{};                  // ill-formed; previously well-formed
B b = {1};              // ill-formed; previously well-formed
auto* c = new C{2, 3};  // ill-formed; previously well-formed

struct Y;

struct X {
  operator Y();
};

struct Y {              // not an aggregate; previously an aggregate
  Y(const Y&) = default;
  X x;
};

Y y{X{}};               // copy constructor call; previously aggregate-initialization

https://godbolt.org/z/946Gs14GP