fix: prevent changing buffer in lazy window

Adds the new `winfixbuf` to the window options of the lazy window. This makes the buffer "sticky", preventing accidentally switching to another buffer while in that window, e.g. via `:edit`. See the PR at nvim core neovim/neovim#12517

`winfixbuf` is only available on newer nvim versions, so adding the option is wrapped in a condition checking whether it is supported.

lua/lazy/view/float.lua

@@ -184,6 +184,9 @@ function M:mount()
     Util.wo(self.win, "wrap", true)
     Util.wo(self.win, "winhighlight", "Normal:LazyNormal")
     Util.wo(self.win, "colorcolumn", "")
+    if vim.fn.exists('&winfixbuf') == 1 then
+      Util.wo(self.win, "winfixbuf", true)
+    end
   end
   opts()