fix: use Go 1.20 on CircleCI

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

This needs slight reformatting to make go fmt happy and the switch from
`GODEBUG=cgocheck=2` to `GOEXPERIMENT=cgocheck2`.

[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:
@@ -353,13 +353,13 @@ commands:
           no_output_timeout: 90m
       - run:
           name: Run the Go tests
-          command: GODEBUG=cgocheck=2 RUST_LOG=info go test -p 1 -timeout 60m
+          command: GOEXPERIMENT=cgocheck2 RUST_LOG=info go test -p 1 -timeout 60m
           no_output_timeout: 60m
   compile_tests:
     steps:
       - run:
           name: Build project and tests, but don't actually run the tests (used to verify that build/link works with Darwin)
-          command: GODEBUG=cgocheck=2 RUST_LOG=info go test -run=^$
+          command: GOEXPERIMENT=cgocheck2 RUST_LOG=info go test -run=^$
   restore_parameter_cache:
     steps:
       - restore_cache:

cgo/types.go

@@ -91,7 +91,7 @@ type PoStProofGo struct {
 	Proof           []byte
 }
 
-/// FvmMachineExecuteResponse is a go allocated version of `FvmMachineExecuteResponse`.
+// FvmMachineExecuteResponse is a go allocated version of `FvmMachineExecuteResponse`.
 type FvmMachineExecuteResponseGo struct {
 	ExitCode             uint64
 	ReturnVal            []byte