patch 8.2.4970: "eval 123" gives an error, "eval 'abc'" does not

Problem:    "eval 123" gives an error, "eval 'abc'" does not.
Solution:   Also give an error when evaluating only a string. (closes #10434)

src/testdir/test_vim9_cmd.vim

@@ -697,6 +697,16 @@ def Test_use_register()
   END
   v9.CheckDefAndScriptFailure(lines, 'E1207:', 2)
   $SomeEnv = ''
+
+  lines =<< trim END
+      eval 'value'
+  END
+  v9.CheckDefAndScriptFailure(lines, 'E1207:', 1)
+
+  lines =<< trim END
+      eval "value"
+  END
+  v9.CheckDefAndScriptFailure(lines, 'E1207:', 1)
 enddef
 
 def Test_environment_use_linebreak()