fix aws-s3 upper bound on base64

[avsm]

cc @hcarty, found in #13388 revdeps

[camelus]

🌤️ opam-lint warnings e158592

• aws-s3.0.9.0 has some warnings:

  • warning 47: Synopsis should start with a capital and not end with a dot

• aws-s3.1.1.0 has some warnings:

  • warning 47: Synopsis should start with a capital and not end with a dot

• aws-s3.1.1.1 has some warnings:

  • warning 47: Synopsis should start with a capital and not end with a dot

• These packages passed lint tests: aws-s3.2.0.0, aws-s3.3.0.0

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☀️ Installability check (10372 → 10372)

[avsm]

This fixing was masking another one with yojson deprecation, so ill fix that separately