fix: use Go 1.20 on CircleCI

As Lotus is now using Go 1.20 [1], I also upgrade this CI to use 1.20.

[1]: filecoin-project/lotus#11347

.circleci/config.yml

@@ -6,7 +6,7 @@ orbs:
 executors:
   golang:
     docker:
-      - image: cimg/go:1.18
+      - image: cimg/go:1.20
     resource_class: small
     environment:
       # Build the kernel only for the single architecture. This should reduce
@@ -234,7 +234,7 @@ commands:
             - run:
                 name: Install Go
                 command: |
-                  curl https://dl.google.com/go/go1.17.9.darwin-amd64.pkg -o /tmp/go.pkg && \
+                  curl https://dl.google.com/go/go1.20.10.darwin-amd64.pkg -o /tmp/go.pkg && \
                   sudo installer -pkg /tmp/go.pkg -target /
                   go version
             - run: