docs: stricter bufname and bufnr types (#27454)

runtime/lua/vim/_meta/vimfn.lua

@@ -582,7 +582,7 @@ function vim.fn.bufloaded(buf) end
 ---   echo bufname("file2")  " name of buffer where "file2" matches.
 --- <
 ---
---- @param buf? any
+--- @param buf? integer|string
 --- @return string
 function vim.fn.bufname(buf) end
 
@@ -599,7 +599,7 @@ function vim.fn.bufname(buf) end
 --- number necessarily exist, because ":bwipeout" may have removed
 --- them.  Use bufexists() to test for the existence of a buffer.
 ---
---- @param buf? any
+--- @param buf? integer|string
 --- @param create? any
 --- @return integer
 function vim.fn.bufnr(buf, create) end

src/nvim/eval.lua

@@ -809,7 +809,7 @@ M.funcs = {
       <
     ]=],
     name = 'bufname',
-    params = { { 'buf', 'any' } },
+    params = { { 'buf', 'integer|string' } },
     returns = 'string',
     signature = 'bufname([{buf}])',
   },
@@ -832,7 +832,7 @@ M.funcs = {
 
     ]=],
     name = 'bufnr',
-    params = { { 'buf', 'any' }, { 'create', 'any' } },
+    params = { { 'buf', 'integer|string' }, { 'create', 'any' } },
     returns = 'integer',
     signature = 'bufnr([{buf} [, {create}]])',
   },