fix(ci): update gocover-cobertura to v1.4.0 for Go 1.24+ compatibility

Update integration test job to use gocover-cobertura v1.4.0 instead of
v1.2.1-0.20240107185409-0818f3538137 to resolve compilation error with
golang.org/x/tools@v0.8.0 on Go 1.24+.

The old version depends on golang.org/x/tools@v0.8.0 which has a bug
causing 'invalid array length' errors in tokeninternal package with Go 1.24+.
Version v1.4.0 uses golang.org/x/tools@v0.29.0 which is compatible.

This completes the fix for integration tests by updating both gotestsum
(already fixed in previous commit) and gocover-cobertura.

Verified:
- Integration tests compile successfully with -tags=integration
- gotestsum v1.13.0 runs without errors
- gocover-cobertura v1.4.0 successfully converts coverage to XML
- Complete tool chain tested with Go 1.25.0

Co-authored-by: Ona <no-reply@ona.com>