build: refine CI and Bump Go Version Requirement

- Update GitHub Actions workflow to test only with Go versions 1.20 and 1.21
- Bump the Go language version requirement from 1.18 to 1.20 in `go.mod`

Signed-off-by: Bo-Yi Wu <[email protected]>

Author: appleboy

.github/workflows/go.yml

@@ -21,7 +21,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        go: [1.18, 1.19, "1.20", 1.21]
+        go: ["1.20", 1.21]
         include:
           - os: ubuntu-latest
             go-build: ~/.cache/go-build

go.mod

@@ -1,6 +1,6 @@
 module github.com/golang-queue/nats
 
-go 1.18
+go 1.20
 
 require (
 	github.com/golang-queue/queue v0.1.4-0.20221230133718-0314ef173f98