Add `ci.yml` github actions workflow.

[azriel91]

Switch CI to use github actions, as bors isn't getting past travis (always times out).

[azriel91]

bors r+

[bors[bot]]

Timed out.

[azriel91]

bors retry

[bors[bot]]

Timed out.

[azriel91]

Not sure what's going on, since the github actions build finishes quickly. May be on the bors application side, or may be our bors configuration.

[azriel91]

bors retry

[bors[bot]]

Timed out.

[azriel91]

bors retry

[azriel91]

bors try

[bors[bot]]

Timed out.

[azriel91]

bors r+

[bors[bot]]

Canceled.

[azriel91]

bors r+

[bors[bot]]

Canceled.

[azriel91]

bors r+

[bors[bot]]

Build succeeded:

• Build and Test (Linux) (beta)
• Build and Test (Linux) (stable)
• Build and Test (Linux) (nightly)
• Build and Test (Linux) (1.38.0)

[bors[bot]]

try

Timed out.