[clang-format] Fix short functions being considered as inline inside an indented namespace.

Fixes https://github.com/llvm/llvm-project/issues/24784.

With config:
```
AllowShortFunctionsOnASingleLine: Inline
NamespaceIndentation: All
```

The code:
```
namespace Test
{
    void f()
    {
        return;
    }
}
```
was incorrectly formatted to:
```
namespace Test
{
    void f() { return; }
}
```

since the function `f` was considered being inside a class/struct/record.
That's because the check was simplistic and only checked for a non-zero indentation level of the line starting `f`.

Reviewed By: MyDeveloperDay, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D117142