Update go directive to 1.23.0

[sahidvelji]

The README states that "The OpenFeature Go SDK only supports currently maintained Go language versions". As such, I suggest that this be made explicit by updating the go directive in go.mod to be 1.23.0. This also aligns with how https://github.com/open-telemetry/opentelemetry-go manages Go versions. For what it's worth, opentelemetry-go dropped support for Go 1.22 in March.

go-sdk/go.mod

Line 3 in 640448d

go 1.21

As part of this change, this line in the README should also be updated:

go-sdk/README.md

Line 46 in 640448d

Go language version: [1.20](https://go.dev/doc/devel/release#go1.20)