This commit improves the behavior of showing the "toggle source" element on mouseover.
For example, when a method has one more signatures by using `:call-seq:`,
```ruby
# :call-seq:
# foo {|element| ... } -> self
# foo -> new_enumeration
def foo
end
```
The current CSS doesn't show "toggle source" even when hovering the second signature `foo -> new_enumeration`.
But this change will show "toggle source" always when hovering over any signature.
For details about the `.method-header` element, see `lib/rdoc/generator/template/darkfish/class.rhtml`:
0e060c69f5/lib/rdoc/generator/template/darkfish/class.rhtml (L101-L124)
For example, see https://docs.ruby-lang.org/en/3.2/Array.html#method-i-delete