chore: support go1.18 and update dependencies (#708)

Here's the squash of the following patches that enable support
for go1.18 and update our dependencies.

This diff WILL need to be backported to the release/3.14 branch.

* chore: use go1.17.8

See https://github.com/ooni/probe/issues/2067

* chore: upgrade to probe-assets@v0.8.0

See https://github.com/ooni/probe/issues/2067.

* chore: update dependencies and enable go1.18

As mentioned in https://github.com/ooni/psiphon/commit/7a0d17ea91f8548dedf32daa07bcc00c1839b5b3,
the tree won't build with `go1.18` unless we say it does.

So, not only here we need to update dependencies but also we
need to explicitly say `go1.18` in the `go.mod`.

This work is part of https://github.com/ooni/probe/issues/2067.

* chore(coverage.yml): run with go1.18

This change will give us a bare minimum confidence that we're
going to build our tree using version 1.18 of golang.

See https://github.com/ooni/probe/issues/2067.

* chore: update user agent used for measuring

See https://github.com/ooni/probe/issues/2067

* chore: run `go generate ./...`

See https://github.com/ooni/probe/issues/2067

* fix(dialer_test.go): make test work with go1.17 and go1.18

1. the original test wanted the dial to fail, so ensure we're not
passing any domain name to exercise dialing not resolving;

2. match the end of the error rather than the whole error string.

Tested locally with both go1.17 and go1.18.

See https://github.com/ooni/probe-cli/pull/708#issuecomment-1096447186

mk

@@ -64,7 +64,7 @@ GOLANG_EXTRA_FLAGS =
 
 #help:
 #help: * GOLANG_VERSION_NUMBER : the expected version number for golang.
-GOLANG_VERSION_NUMBER = 1.17.6
+GOLANG_VERSION_NUMBER = 1.17.8
 
 #help:
 #help: * MINGW_W64_VERSION     : the expected mingw-w64 version.
@@ -72,7 +72,7 @@ MINGW_W64_VERSION = 10.3.1
 
 #help:
 #help: * OONIGO_BRANCH         : the github.com/ooni/go branch to use.
-OONIGO_BRANCH = oonigo1.17.6
+OONIGO_BRANCH = oonigo1.17.8
 
 #help:
 #help: * OONI_PSIPHON_TAGS     : build tags for `go build -tags ...` that cause