Ignore bindgen generated modules for codecov purposes

Modules generated by bindgen.rs do not contain any logic, but rather
just define structs, constants, etc. However, bindgen does generate a
lot of tests for these for example to check alignment and size. The
problem here is that it does not put these into a `mod test` behind a
`cfg(test)`, meaning code coverage tooling picks them up as production
code. This means that all `assert!` statements are marked as partially
uncovered, resulting in reported code coverage for these files (that
don't even contain any logic) to be 30%.

Thus, exclude these files from the coverage reports.

Signed-off-by: Patrick Roy <roypat@amazon.co.uk>

Author: roypat

tests/integration_tests/build/test_coverage.py

@@ -63,6 +63,7 @@ def test_coverage(monkeypatch):
             --ignore "**/test_utils*" \
             --ignore "**/mock_*" \
             --ignore "src/firecracker/examples/*" \
+            --ignore "**/gen*" \
             -t lcov \
             --ignore-not-existing \
             -o {lcov_file}"""