bug#37452: 26.3; skip-syntax-forward doesn't work in python-mode

[Amai Kinono]

Here's how to reproduce:

- Run `emacs -Q`

- Define a command like this and eval it

  ``` emacs-lisp
  (defun skip-syntax ()
    (interactive)
    (skip-syntax-forward (char-to-string (char-syntax (char-after)))))
  ```

  It gets the syntax of the next char and skip chars with the same syntax.

- M-x python-mode, clear the buffer, type

  ``` python
  print(|'hello')
  ```
 
  `|` stands for the cursor position.

- Call skip-syntax. The expected behavior is:

  ``` python
  print('|hello')
  ```

  but actually the cursor doesn't move.


I've tried some other modes, and the above command can skip the
quotation mark normally, so this should be a problem of Python mode.

In GNU Emacs 26.3 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.10)
 of 2019-08-30 built on juergen
Windowing system distributor 'The X.Org Foundation', version 11.0.12005000
System Description: Manjaro Linux

Recent messages:
uncompressing python.el.gz...
uncompressing python.el.gz...done
Note: file is write protected
Quit [2 times]
M-SPC r is undefined

Configured using:
 'configure --prefix=/usr --sysconfdir=/etc --libexecdir=/usr/lib
 --localstatedir=/var --with-x-toolkit=gtk3 --with-xft --with-modules
 'CFLAGS=-march=x86-64 -mtune=generic -O2 -pipe -fno-plt'
 CPPFLAGS=-D_FORTIFY_SOURCE=2
 LDFLAGS=-Wl,-O1,--sort-common,--as-needed,-z,relro,-z,now'

Configured features:
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Important settings:
  value of $LC_MONETARY: zh_CN.UTF-8
  value of $LC_NUMERIC: zh_CN.UTF-8
  value of $LC_TIME: zh_CN.UTF-8
  value of $LANG: zh_CN.utf8
  value of $XMODIFIERS: @im=fcitx
  locale-coding-system: utf-8-unix

Major mode: Emacs-Lisp

Minor modes in effect:
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  buffer-read-only: t
  line-number-mode: t
  transient-mark-mode: t

Load-path shadows:
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/home/kino/.emacs.d/straight/build/let-alist/let-alist hides /usr/share/emacs/26.3/lisp/emacs-lisp/let-alist
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~/.emacs.d/modules/ui/appearance/config hides ~/.emacs.d/modules/ui/evil/config
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~/.emacs.d/modules/ui/appearance/config hides ~/.emacs.d/modules/ui/window-buffer/config
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~/.emacs.d/modules/ui/appearance/config hides ~/.emacs.d/modules/ide/help/config
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~/.emacs.d/modules/ui/appearance/config hides ~/.emacs.d/modules/app/qrcode/config
~/.emacs.d/modules/ui/appearance/config hides ~/.emacs.d/modules/app/esup/config

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