bump to go 1.20 (#529)

Reviewed-on: https://gitea.com/gitea/tea/pulls/529
Reviewed-by: Lunny Xiao <xiaolunwen@gmail.com>

.drone.yml

@@ -9,7 +9,7 @@ platform:
 steps:
 - name: vendor
   pull: always
-  image: golang:1.18
+  image: golang:1.20
   environment:
     GOPROXY: https://goproxy.io # proxy.golang.org is blocked in China, this proxy is not
   commands:
@@ -17,7 +17,7 @@ steps:
 
 - name: build
   pull: always
-  image: golang:1.18
+  image: golang:1.20
   environment:
     GOPROXY: https://goproxy.io # proxy.golang.org is blocked in China, this proxy is not
   commands:
@@ -34,7 +34,7 @@ steps:
     - pull_request
 
 - name: unit-test
-  image: golang:1.18
+  image: golang:1.20
   commands:
   - make unit-test-coverage
   settings:
@@ -49,7 +49,7 @@ steps:
     - pull_request
 
 - name: release-test
-  image: golang:1.18
+  image: golang:1.20
   commands:
   - make test
   settings:
@@ -65,7 +65,7 @@ steps:
 
 - name: tag-test
   pull: always
-  image: golang:1.18
+  image: golang:1.20
   commands:
   - make test
   settings:
@@ -77,7 +77,7 @@ steps:
     - tag
 
 - name: static
-  image: golang:1.18
+  image: golang:1.20
   environment:
     GOPROXY: https://goproxy.io # proxy.golang.org is blocked in China, this proxy is not
   commands: