Fix typo in ARCHITECTURE.md: "Ann" to "An"

[CECILIA-MULANDI]

I found a slight typo in this line: "Ann approximation of the build command it will execute is:" It should be "An approximation of the build command it will execute is:"

Summary

Closes #_

• y/n | Does it introduce breaking changes?
• y/n | Is it dependent on a specific version of cargo-contract or pallet-revive?

Description

Checklist before requesting a review

• I have added an entry to CHANGELOG.md
• I have commented on my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works
• Any dependent changes have been merged and published in downstream modules