Switch to Go 1.20

It has errors.Join() function which will be used in followup commits.

And also run go mod tidy.

go.mod

@@ -1,22 +1,22 @@
 module github.com/canonical/chisel
 
-go 1.18
+go 1.20
 
 require (
+	github.com/blakesmith/ar v0.0.0-20190502131153-809d4375e1fb
+	github.com/jessevdk/go-flags v1.5.0
+	github.com/juju/fslock v0.0.0-20160525022230-4d5c94c67b4b
+	github.com/klauspost/compress v1.15.4
+	github.com/ulikunitz/xz v0.5.10
+	go.starlark.net v0.0.0-20220328144851-d1966c6b9fcd
+	golang.org/x/crypto v0.0.0-20220518034528-6f7dac969898
 	gopkg.in/check.v1 v1.0.0-20201130134442-10cb98267c6c
 	gopkg.in/yaml.v3 v3.0.0-20220512140231-539c8e751b99
 )
 
 require (
-	github.com/blakesmith/ar v0.0.0-20190502131153-809d4375e1fb // indirect
-	github.com/jessevdk/go-flags v1.5.0 // indirect
-	github.com/juju/fslock v0.0.0-20160525022230-4d5c94c67b4b // indirect
-	github.com/klauspost/compress v1.15.4 // indirect
 	github.com/kr/pretty v0.2.1 // indirect
 	github.com/kr/text v0.1.0 // indirect
-	github.com/ulikunitz/xz v0.5.10 // indirect
-	go.starlark.net v0.0.0-20220328144851-d1966c6b9fcd // indirect
-	golang.org/x/crypto v0.0.0-20220518034528-6f7dac969898 // indirect
 	golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1 // indirect
 	golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1 // indirect
 )

go.sum

@@ -60,7 +60,6 @@ golang.org/x/sys v0.0.0-20180830151530-49385e6e1522/go.mod h1:STP8DvDyc/dI5b8T5h
 golang.org/x/sys v0.0.0-20190215142949-d0b11bdaac8a/go.mod h1:STP8DvDyc/dI5b8T5hshtkjS+E42TnysNCUPdjciGhY=
 golang.org/x/sys v0.0.0-20200930185726-fdedc70b468f/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
-golang.org/x/sys v0.0.0-20210320140829-1e4c9ba3b0c4 h1:EZ2mChiOa8udjfp6rRmswTbtZN/QzUQp4ptM4rnjHvc=
 golang.org/x/sys v0.0.0-20210320140829-1e4c9ba3b0c4/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1 h1:SrN+KX8Art/Sf4HNj6Zcz06G7VEz+7w9tdXTPOZ7+l4=
 golang.org/x/sys v0.0.0-20210615035016-665e8c7367d1/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=