go1.23 isn't a valid toolchain

[Firepup6500]

It should be 1.23.0, otherwise running make fails because go cannot find the toolchain it has been told to get.

Un-edited:

firepup650@firepi:~/projects/go/irc-slack/cmd/irc-slack $ go version
go: downloading go1.23 (linux/arm64)
go: download go1.23 for linux/arm64: toolchain not available
firepup650@firepi:~/projects/go/irc-slack/cmd/irc-slack $ 

Edited go.mod to specify 1.23.0:

firepup650@firepi:~/projects/go/irc-slack/cmd/irc-slack $ go version
go: downloading go1.23.0 (linux/arm64)
go version go1.23.0 linux/arm64
firepup650@firepi:~/projects/go/irc-slack/cmd/irc-slack $