CI: fix gem-test-java job

[flavorjones]

The gem-test-java job has never been stable, but I tried to make sure it would use the version-under-test in 1f0d41c. Since that commit, we had Hoe issues (see 6c6a8a7) and racc issues (see ruby/racc#125).

Now, we're seeing what I think is a real failure of the version-under-test changes from 1f0d41c, and it's blocking PRs from going green:

(from https://ci.nokogiri.org/teams/nokogiri-core/pipelines/nokogiri-pr/jobs/gem-test-java/builds/47)

+ pushd gems
/tmp/build/3c897710/gems /tmp/build/3c897710
++ ls nokogiri-2020.0115.0138-java.gem
++ head -n1
+ gemfile=nokogiri-2020.0115.0138-java.gem
+ sha256sum nokogiri-2020.0115.0138-java.gem
9de938110aec26ae3460ec456f8fa043c1e204d9f6affa4869857a05479fa66a  nokogiri-2020.0115.0138-java.gem
+ gem install nokogiri-2020.0115.0138-java.gem
Successfully installed nokogiri-2020.0115.0138-java
1 gem installed
+ gem list -d nokogiri

*** LOCAL GEMS ***

nokogiri (2020.0115.0138)
    Platform: java
    Authors: Aaron Patterson, Mike Dalessio, Yoko Harada, Tim Elliott,
    Akinori MUSHA, John Shahid, Lars Kanis
    Homepage: https://nokogiri.org
    License: MIT
    Installed at: /usr/local/bundle

    Nokogiri (鋸) is an HTML, XML, SAX, and Reader parser
+ nokogiri -v
# Nokogiri (2020.0115.0138)
    ---
    warnings: []
    nokogiri: 2020.0115.0138
    ruby:
      version: 2.5.7
      platform: java
      description: jruby 9.2.9.0 (2.5.7) 2019-10-30 458ad3e OpenJDK 64-Bit Server VM 25.232-b09
        on 1.8.0_232-b09 +jit [linux-x86_64]
      engine: jruby
      jruby: 9.2.9.0
    xerces: Xerces-J 2.12.0
    nekohtml: NekoHTML 1.9.21
+ popd
/tmp/build/3c897710
+ pushd nokogiri
/tmp/build/3c897710/nokogiri /tmp/build/3c897710
++ pwd
+ export BUNDLE_GEMFILE=/tmp/build/3c897710/nokogiri/Gemfile
+ BUNDLE_GEMFILE=/tmp/build/3c897710/nokogiri/Gemfile
+ bundle -v
Bundler version 2.1.4
+ bundle config
Settings are listed in order of priority. The top value will be used.
path
Set via BUNDLE_PATH: "/usr/local/bundle"

app_config
Set via BUNDLE_APP_CONFIG: "/usr/local/bundle"

silence_root_warning
Set via BUNDLE_SILENCE_ROOT_WARNING: true

gemfile
Set via BUNDLE_GEMFILE: "/tmp/build/3c897710/nokogiri/Gemfile"

bin
Set via BUNDLE_BIN: "/usr/local/bundle/bin"

+ bundle add nokogiri --skip-install
Fetching gem metadata from https://rubygems.org/.................
Resolving dependencies......................................................
+ bundle install --local
Resolving dependencies......
Could not find hoe-3.21.0 in any of the sources
+ bundle install
Fetching gem metadata from https://rubygems.org/.................
Resolving dependencies........
Your bundle is locked to nokogiri (2020.0115.0138-java), but that version could
not be found in any of the sources listed in your Gemfile. If you haven't
changed sources, that means the author of nokogiri (2020.0115.0138-java) has
removed it. You'll need to update your bundle to a version other than nokogiri
(2020.0115.0138-java) that hasn't been removed in order to install.

[flavorjones]

I think this is resolved now.