fix ci: upgrade go to 1.20

[zxh326]

to fix ci

 > [builder 13/13] RUN cd /workspace && git clone --branch=main https://github.com/juicedata/juicefs &&     cd juicefs && git checkout main &&     bash -c "if [[ amd64 == amd64 ]]; then make juicefs.all && mv juicefs.all juicefs; else make juicefs; fi":
13.36 go: downloading github.com/google/go-cmp v0.6.0
13.37 go: downloading github.com/hashicorp/golang-lru v0.5.4
13.38 go: downloading github.com/tidwall/gjson v1.9.3
13.39 go: downloading github.com/tidwall/sjson v1.0.4
13.40 go: downloading github.com/tidwall/match v1.1.1
13.40 go: downloading github.com/tidwall/pretty v1.2.0
101.2 # github.com/juicedata/juicefs/pkg/meta
101.2 pkg/meta/base.go:162:27: symCache.Swap undefined (type *symlinkCache has no field or method Swap)
101.2 note: module requires Go 1.20
106.2 make: *** [Makefile:44: juicefs.all] Error 2

/cc @zwwhdls