Fix method name in S3 AsciiDoc

[manakbisht]

This is most definitely a typo, the correct method is S3Template#createSignedGetURL.

:loudspeaker: Type of change

• [ ] Bugfix
• [ ] New feature
• [x] Enhancement
• [ ] Refactoring

:scroll: Description

The current AsciiDoc refers to a non-existent method S3Template#createSignedGetUrl.

:bulb: Motivation and Context

Corrects documentation.

:green_heart: How did you test it?

No code changes.

:pencil: Checklist

• [x] I reviewed submitted code
• [ ] I added tests to verify changes
• [ ] I updated reference documentation to reflect the change
• [ ] All tests passing
• [x] No breaking changes

:crystal_ball: Next steps