go: Manually upgrade minimum go version in go.mod

Manually upgrade minimum go version in go.mod to 1.21 to align with
hermit installed go version.

Author: juliaogris

go.mod

@@ -1,5 +1,5 @@
 module foxygo.at/evy
 
-go 1.20
+go 1.21
 
 require github.com/alecthomas/kong v0.8.0

go.sum

@@ -1,5 +1,8 @@
 github.com/alecthomas/assert/v2 v2.1.0 h1:tbredtNcQnoSd3QBhQWI7QZ3XHOVkw1Moklp2ojoH/0=
+github.com/alecthomas/assert/v2 v2.1.0/go.mod h1:b/+1DI2Q6NckYi+3mXyH3wFb8qG37K/DuK80n7WefXA=
 github.com/alecthomas/kong v0.8.0 h1:ryDCzutfIqJPnNn0omnrgHLbAggDQM2VWHikE1xqK7s=
 github.com/alecthomas/kong v0.8.0/go.mod h1:n1iCIO2xS46oE8ZfYCNDqdR0b0wZNrXAIAqro/2132U=
 github.com/alecthomas/repr v0.1.0 h1:ENn2e1+J3k09gyj2shc0dHr/yjaWSHRlrJ4DPMevDqE=
+github.com/alecthomas/repr v0.1.0/go.mod h1:2kn6fqh/zIyPLmm3ugklbEi5hg5wS435eygvNfaDQL8=
 github.com/hexops/gotextdiff v1.0.3 h1:gitA9+qJrrTCsiCl7+kh75nPqQt1cx4ZkudSTLoUqJM=
+github.com/hexops/gotextdiff v1.0.3/go.mod h1:pSWU5MAI3yDq+fZBTazCSJysOMbxWL1BSow5/V2vxeg=