Change max length of SKU to 255

[lex111]

I want to merge this change because...

Resolves #4389

Pull Request Checklist

1. Privileged views and APIs are guarded by proper permission checks.
2. All visible strings are translated with proper context.
3. All data-formatting is locale-aware (dates, numbers, and so on).
4. Database queries are optimized and the number of queries is constant.
5. Database migration files are up to date.
6. The changes are tested.
7. GraphQL schema and type definitions are up to date.
8. Changes are mentioned in the changelog.

[django-queries]

Here is the report for 0691c00 (lex111/saleor @ sku-255)
Base comparison is d54fd99.

No differences were found. (click me)

# api.benchmark checkout
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  add billing address to checkout            	         34	         34	             20
  add shipping to checkout                   	          7	          7	              0
  checkout payment charge                    	         14	         14	              0
  complete checkout                          	          6	          6	              0
  create checkout                            	         48	         48	             24

# api.benchmark homepage
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  retrieve main menu                         	          5	          5	              0
  retrieve product list                      	          4	          4	              0
  retrieve secondary menu                    	          5	          5	              0
  retrieve shop                              	          2	          2	              0

# api.benchmark product
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  product details                            	         15	         15	              3
  retrieve product attributes                	         13	         13	              2

# api.benchmark variant
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  retrieve variant list                      	         18	         18	              8

# api product sorting attributes
  test name                                  	left count 	right count	duplicate count
  -------------------------------------------	-----------	-----------	---------------
  sort product not having attribute data     	         21	         21	              0

[maarcingebala]

Thanks for opening the PR! Changes look good but there are two minor things to fix:

• please apply Black to your changes (it's failing on CI now),
• update the CHANGELOG.md by adding an entry in the "Unreleased" section with the description of your changes, a number of the PR and you Github handle (see at other entries).

[codecov]

Codecov Report

Merging #4811 into master will not change coverage.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master    #4811   +/-   ##
=======================================
  Coverage   91.24%   91.24%           
=======================================
  Files         344      344           
  Lines       20616    20616           
  Branches     1956     1956           
=======================================
  Hits        18812    18812           
  Misses       1266     1266           
  Partials      538      538

Impacted Files	Coverage Δ
saleor/order/models.py	90.98% <100%> (ø)	⬆️
saleor/product/models.py	93.77% <100%> (ø)	⬆️

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[maarcingebala]

🎉 Thanks for your contribution and for participating in Hacktoberfest! Please send me your shipping address to marcin@mirumee.com and we'll send you our Ultra-Fast Socks:

[lex111]

@maarcingebala thanks to you, too! I really wanted to update Russian localization, there are enough mistakes, but I can not test this locally via Docker. I understand that you are using Transifex, but I cannot change and see update locale? In general, would it be easier for me to open a PR with my edits rather than to do this on Transifex, or can I upload my file (*.po) into this service?

[NyanKiyoshi]

@lex111 I believe you should be able to do it, I don't think there are special permissions to be able to. That's how I used to do: https://docs.transifex.com/translation/importing-translations

[lex111]

@NyanKiyoshi cool, I’ll definitely try when I finish the translation. But it’s bad that now I can’t see my changes locally :(