go.mod: minimum Go version 1.18 (#26160)

This will allow use of generics and other new standard library APIs
such as package net/netip.

README.md

@@ -16,7 +16,7 @@ archives are published at https://geth.ethereum.org/downloads/.
 
 For prerequisites and detailed build instructions please read the [Installation Instructions](https://geth.ethereum.org/docs/install-and-build/installing-geth).
 
-Building `geth` requires both a Go (version 1.16 or later) and a C compiler. You can install
+Building `geth` requires both a Go (version 1.18 or later) and a C compiler. You can install
 them using your favourite package manager. Once the dependencies are installed, run
 
 ```shell

go.mod

@@ -1,6 +1,6 @@
 module github.com/ethereum/go-ethereum
 
-go 1.17
+go 1.18
 
 require (
 	github.com/Azure/azure-sdk-for-go/sdk/storage/azblob v0.3.0