fix(pack): add trailing newline to lockfile #38469

Problem: JSON files should end with a trailing newline so that Unix
  tools work as expected, Git doesn't report "No newline at end of file"
  and to avoid noise in diffs from editors and other tools adding the
  missing newline.

Solution: Add trailing newline.

runtime/lua/vim/pack.lua

@@ -819,7 +819,7 @@ local function lock_write()
   local fd = assert(uv.fs_open(path, 'w', 438))
 
   local data = vim.json.encode(lock, { indent = '  ', sort_keys = true })
-  assert(uv.fs_write(fd, data))
+  assert(uv.fs_write(fd, data .. '\n'))
   assert(uv.fs_close(fd))
 end
 

test/functional/plugin/pack_spec.lua

@@ -574,7 +574,8 @@ describe('vim.pack', function()
               "version": ">=0.0.0"
             }
           }
-        }]]):format(
+        }
+        ]]):format(
         basic_rev,
         repos_src.basic,
         defbranch_rev,