ci: bump to go 1.20 (#375)

* Update CI Go version to 1.20/1.19
* Update `golangci-lint` to v1.51.2
* Update coverage collection to use new Go 1.20 tools
* Update coverage job to only run on latest Go version

Fixes #367

.github/workflows/thirdparty.yml

@@ -18,7 +18,7 @@ jobs:
       - name: Install Go
         uses: actions/setup-go@c4a742cab115ed795e34d4513e2cf7d472deb55f # v3.3.1
         with:
-          go-version: 1.19.x
+          go-version: 1.20.x
           check-latest: true
       - name: Checkout code
         uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8 # v3.1.0