CI: added x86 workflow

[obfusk]

Fixes #559.

Seems to work: https://github.com/obfusk/pyjnius/actions/runs/320541517

NB: this adds working CI for x86 linux; #536 fixes the rest.

Also: I tried using the checkout action but that failed in the docker container, so I duplicated its git commands.

[cmacdonald]

LGTM

[tshirtman]

arf, seems it failed after merging…

E   RuntimeError: 
E           Unable to find libjvm.so, (tried ['/opt/hostedtoolcache/jdk/8.0.265/x86/lib/server/libjvm.so', '/opt/hostedtoolcache/jdk/8.0.265/x86/jre/lib/amd64/default/libjvm.so', '/opt/hostedtoolcache/jdk/8.0.265/x86/jre/lib/amd64/server/libjvm.so'])
E           you can use the JVM_PATH env variable with the relative path
E           from JAVA_HOME to libjvm.so to override this lookup, if you know
E           where pyjnius should look for it.
E   

so env doesn't find the proper java env…

ah no, that will be fixed by the other PR as you mentionned.