go.mod: upgrade to Go 1.21 min

Fixes #6. Follows version policy change in nspcc-dev/.github#30.

Signed-off-by: Roman Khimov <roman@nspcc.ru>

.github/workflows/run_tests.yml

@@ -44,20 +44,14 @@ jobs:
     runs-on: ${{ matrix.os }}
     strategy:
       matrix:
-        go_versions: [ '1.20', '1.21', '1.22' ]
+        go_versions: [ '1.21', '1.22' ]
         os: [ubuntu-22.04, windows-2022, macos-12, macos-14]
         exclude:
           # Only latest Go version for Windows and MacOS.
-          - os: windows-2022
-            go_versions: '1.20'
           - os: windows-2022
             go_versions: '1.21'
-          - os: macos-12
-            go_versions: '1.20'
           - os: macos-12
             go_versions: '1.21'
-          - os: macos-14
-            go_versions: '1.20'
           - os: macos-14
             go_versions: '1.21'
           # Exclude latest Go version for Ubuntu as Coverage uses it.

go.mod

@@ -1,4 +1,4 @@
 module github.com/nspcc-dev/go-ordered-json
 
-go 1.20
+go 1.21