ci: update Go version to 1.20 and adjust GitHub Actions accordingly

- Remove support for Go 1.18 and 1.19 in GitHub Actions workflow
- Update Go version in `go.mod` from 1.18 to 1.20

Signed-off-by: appleboy <[email protected]>

Author: appleboy

.github/workflows/go.yml

@@ -22,7 +22,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        go: [1.18, 1.19, "1.20", 1.21, 1.22, 1.23]
+        go: ["1.20", 1.21, 1.22, 1.23]
         include:
           - os: ubuntu-latest
             go-build: ~/.cache/go-build

go.mod

@@ -1,6 +1,6 @@
 module github.com/golang-queue/redisdb
 
-go 1.18
+go 1.20
 
 require (
 	github.com/golang-queue/queue v0.1.4-0.20221210024521-cb8720b0c721