Ensure code stays compatible with the Go version in go.mod

[jsoriano]

#1335 included the use of a new function introduced in 1.25, though go.mod announced compatibility with 1.24. This passed unnoticed till a user tried to build the project using 1.24. The change was then reverted in #1567.

CI uses the version in .go-version, so it is not really testing the code with the same version as the one declared in go.mod.

The project is not specially intended to be used as module, but in any case it would be nice to keep Go code compatible with what is declared in go.mod.

We should do one of these:

• Support a single minor, and ensure that .go-version remains aligned with the minor of the go version declared in go.mod.
• Support multiple minors, and keep a CI matrix to at least build and run unit tests with all the minors supported.