Prevent early, spurious Codecov reports (#972)

* Prevent early, spurious Codecov reports

* Fix after_n_builds to be for comment instead of notify

It turns out comment is for email and notify is for Slack, IRC, etc:
https://docs.codecov.io/docs/notifications

* Separate test and lint jobs

* Move after_n_builds into tests flag

* Revert commits

This reverts commit 64ebab0 and
everything after it.

* Change codecov back to reporting after all 14 builds

* Increase after_n_builds to include codecov builds itself

* Address codecov comments

Author: LWprogramming

codecov.yml

@@ -5,3 +5,5 @@ coverage:
         target: auto
         threshold: 0.03%
         base: auto
+comment:
+  after_n_builds: 14 # Prevent early, spurious Codecov reports before all tests finish: https://github.com/kensho-technologies/graphql-compiler/pull/806#issuecomment-730622647. 14 is calculated from the number of jobs to run, which is specified in the .github/workflows/tests_and_lint.yml file: 6 lint jobs (1 job per combination of python-version and lint-flags) and 8 test jobs (1 job per combination of python-version and markers).