Update minimum Git version to v2.24

What does this MR do?

Updates source installation docs to mention the correct Git minimum supported version (v2.24) based on recent changes made to Gitaly (gitaly!2192 (comment 345646144)). Also bumps the minimum Go version based on Gitaly requirements.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

Low risk, only a doc change.