Tweak build workflow

[lebrice]

• Make it so the build workflow doesn't run on changes to the README (as is the case in #122 )
• The build workflow will now have a concurrency setting to cancel previous workflow runs on a push to the same branch.
• Pass the codecov token explicitly to fix issues with codecov upload step
• Increase the length allowed for integration tests

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 72.93%. Comparing base (c74ee6d) to head (ed1714f).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #123 +/- ## ======================================= Coverage 72.93% 72.93% ======================================= Files 15 15 Lines 2176 2176 ======================================= Hits 1587 1587 Misses 589 589 ``` | [Flag](https://app.codecov.io/gh/mila-iqia/milatools/pull/123/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | Coverage Δ | | |---|---|---| | [integrationtests](https://app.codecov.io/gh/mila-iqia/milatools/pull/123/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `?` | | | [unittests](https://app.codecov.io/gh/mila-iqia/milatools/pull/123/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia) | `?` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=mila-iqia#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.