Correct context env max to match with english document

[nanophate]

Description

Japanese document stated that max env length is 3,200 but actually we support until 32,000.

https://circleci.com/docs/contexts/#contexts-and-environment-variable-constraints:~:text=An%20environment%20variable%20value%20must%20have%2032k%20or%20fewer%20characters.

Reasons

Customer in JAPAC region mentioned about this issue and were confused.

Content Checklist

Please follow our style when contributing to CircleCI docs. Our style guide is here: https://circleci.com/docs/style/style-guide-overview.

Please take a moment to check through the following items when submitting your PR (this is just a guide so will not be relevant for all PRs) 😸:

• Break up walls of text by adding paragraph breaks.
• Consider if the content could benefit from more structure, such as lists or tables, to make it easier to consume.
• Keep the title between 20 and 70 characters.
• Consider whether the content would benefit from more subsections (h2-h6 headings) to make it easier to consume.
• Check all headings h1-h6 are in sentence case (only first letter is capitalized).
• Is there a "Next steps" section at the end of the page giving the reader a clear path to what to read next?
• Include relevant backlinks to other CircleCI docs/pages.