[Backport release-0.9] fix(loader): reset hashes when running the loader (#23181)

fix(loader): only keep hashes for the current loop iteration

(cherry picked from commit e12cfa567f)

Co-authored-by: Lewis Russell <lewis6991@gmail.com>

test/functional/lua/loader_spec.lua

@@ -0,0 +1,36 @@
+-- Test suite for testing interactions with API bindings
+local helpers = require('test.functional.helpers')(after_each)
+
+local exec_lua = helpers.exec_lua
+local command = helpers.command
+local eq = helpers.eq
+
+describe('vim.loader', function()
+  before_each(helpers.clear)
+
+  it('handles changing files (#23027)', function()
+    exec_lua[[
+      vim.loader.enable()
+    ]]
+
+    local tmp = helpers.tmpname()
+    command('edit ' .. tmp)
+
+    eq(1, exec_lua([[
+      vim.api.nvim_buf_set_lines(0, 0, -1, true, {'_G.TEST=1'})
+      vim.cmd.write()
+      loadfile(...)()
+      return _G.TEST
+    ]], tmp))
+
+    -- fs latency
+    helpers.sleep(10)
+
+    eq(2, exec_lua([[
+      vim.api.nvim_buf_set_lines(0, 0, -1, true, {'_G.TEST=2'})
+      vim.cmd.write()
+      loadfile(...)()
+      return _G.TEST
+    ]], tmp))
+  end)
+end)