Upgrade codecov-action version. (#92)
Codecov recently announced an issue with their bash upload script. Details of the incident can be found at https://about.codecov.io/security-update/ In order to help protect against similar future issues, the codecov-action was first updated in 1.4.0 to verify the script after downloading and in 1.5.0 the current version of the upload script has been vendored into the action. Workflows which specify the `@v1` tag will automatically use the latest 1.x version of the action as long as codecov continue to update the v1 tag. Since this workflow uses pinned action versions I have updated the version to 1.5.0. Any version >=1.4.0 is sufficient to verify the upload script but since 1.5.0 is the latest version as of now I decided to bump to it.