[clang-tools-extra] [clang-tidy] Fix false positive in `bugprone-std-namespace-modification` when opening subnamespaces of `std::` (PR #174170)

[Victor Chernyakin via cfe-commits]

localspook wrote:

It looks like using an inline namespace is exactly what libc++ does. But even with libc++, the following code compiles just fine (https://godbolt.org/z/PYz5aafvv):

```cpp
#include <ranges>

struct MyClass1 {};
struct MyClass2 {};

namespace std::ranges {

template <> constexpr bool enable_view<MyClass1> = true;

}

namespace std { namespace ranges {

template <> constexpr bool enable_view<MyClass2> = true;

} }
```
Is this guaranteed to work by the standard? If not, it seems like a really unexpected footgun

https://github.com/llvm/llvm-project/pull/174170