python3-pbr: upgrade 5.10.0 -> 5.11.0

Changelog:
=========
* Fix symbol identification in multiline message
* Replace deprecated readfp method with read\_file

Signed-off-by: Zheng Ruoqin <zhengrq.fnst@fujitsu.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>