docs: inconsistent Go version requirement between source docs and site docs.

[mchmarny]

inconsistent Go version requirement between source docs and site docs.
- docs/user/installation.md:70 says Go 1.26 or higher.
- site/content/docs/user/installation.md:75 says Go 1.25 or higher.

Originally posted by @yuanchen8911 in #357 (review)