flake/coverage: remove -Cstrip=none rust flag

[marijanp]

The pipeline for 53899b1 should fail (see pipeline error)

After updating to tarpaulin 0.28 (see release notes, which is achieved by updating nixpkgs, this flag is not required anymore (see succeeding build)

[github-actions]

File	Coverage
All files	67%	✅
kairos-server/src/routes/deposit.rs	86%	✅
kairos-server/src/routes/transfer.rs	73%	✅
kairos-server/src/routes/withdraw.rs	91%	✅
kairos-server/src/config.rs	0%	❌
kairos-server/src/errors.rs	16%	❌
kairos-server/src/utils.rs	22%	❌
kairos-server/tests/transactions.rs	83%	✅
kairos-test-utils/src/cctl/parsers.rs	55%	❌
kairos-crypto/src/implementations/casper.rs	6%	❌
kairos-test-utils/src/cctl.rs	89%	✅
kairos-contracts/demo-contract-tests/tests/test_fixture/mod.rs	93%	✅
kairos-tx/src/asn.rs	71%	✅
kairos-tx/src/error.rs	0%	❌

Minimum allowed coverage is 60%

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