Conform to 1.23 format for go version in go.mod

[ArnaudBrousseau]

Currently:

go get -d ./...
go: errors parsing go.mod:
/Users/arnaud/git/zkBank/go.mod:3: invalid go version '1.21.7': must match format 1.23

After this change things work fine:

go get -d ./...
go: downloading github.com/consensys/gnark v0.9.2-0.20240124123439-9627e98d814f
go: downloading github.com/consensys/gnark-crypto v0.12.2-0.20231221171913-5d5eded6bb15
go: downloading github.com/fxamacker/cbor/v2 v2.5.0
go: downloading github.com/rs/zerolog v1.30.0
go: downloading github.com/blang/semver/v4 v4.0.0
go: downloading github.com/bits-and-blooms/bitset v1.8.0
go: downloading golang.org/x/sys v0.15.0
go: downloading github.com/ingonyama-zk/iciclegnark v0.1.0
go: downloading golang.org/x/exp v0.0.0-20230817173708-d852ddb80c63
go: downloading github.com/google/pprof v0.0.0-20230817174616-7a8ec2ada47b
go: downloading github.com/x448/float16 v0.8.4
go: downloading github.com/mattn/go-isatty v0.0.19
go: downloading github.com/ingonyama-zk/icicle v0.0.0-20230928131117-97f0079e5c71

EDIT: go.sum was dirty after dependency install, committed the diff in another commit. Feel free to discard or keep it :)