clang-tidy warns on use of C-style cast when assigning from an enum value template parameter

https://cxx.godbolt.org/z/hMTPzW7Mq

```cpp
enum E {
Foo
};

template
constexpr E ETemplate = Value;

auto F() -> auto {
[[maybe_unused]] auto a = ETemplate;
}
```

Produces the tidy warning:
```
:6:25: warning: C-style casts are discouraged; use static_cast [google-readability-casting]
6 | constexpr E ETemplate = Value;
| ^
| static_cast<>( )
1 warning generated.
```

This was not the case in clang-19 at least, but it is in 23 and trunk.

It appears that clang is synthesizing a cast to/from the enum value and choosing to do so with a C-style case, and clang-tidy is finding that.

Start with the Compiler Explorer reproduction at https://cxx.godbolt.org/z/hMTPzW7Mq and compare the clang-tidy warning under clang-19, clang-23, and trunk. Trace the synthesized enum conversion responsible for the C-style cast; done means the valid template assignment no longer produces the google-readability-casting warning.

Written by the indexing model from the issue text.