chore: upgrade to go1.18.2 (#750)

I have not upgraded ooni/go yet because I am also checking whether it
would be possible instead to use ooni/oocrypto as documented in the
https://github.com/ooni/probe/issues/2106 issue.

Closes https://github.com/ooni/probe/issues/2070

Closes https://github.com/ooni/probe/issues/2077

.github/workflows/tarball.yml

@@ -16,7 +16,7 @@ jobs:
       - name: Set up Go
         uses: actions/setup-go@v2
         with:
-          go-version: 1.17.10
+          go-version: "1.18.2"
       - name: Generate release tarball
         run: |
           VERSION=${GITHUB_REF_NAME#v}