Add GitHub action to run tests

[jameshadfield]

This workflow was originally implemented as part of #668, but I've split it into a separate PR to debug the failing tests. (Note that tests pass locally on my machine.)

Observed failures (so far...)

• The remote-inputs-uncompressed test uses the input data/references_metadata.tsv and the following (seemingly stochastic) error was observed on GitHub runner:

python3 scripts/sanitize_metadata.py  --metadata data/references_metadata.tsv   ...
Traceback (most recent call last):
...
_csv.Error: Could not determine delimiter

• The remote-inputs-compressed has filtering steps which remove all sequences, thus causing a test failure.

• If the AWS keys are not needed, then we should remove them from the workflow. Note that AWS_DEFAULT_REGION: us-east-1 is needed when running on GitHub actions.