(dbg) add test for flags.py

[MementoRC]

Trying to figure out why the build failed on windows.

CONTEXT_SIGN and CONTEXT_VERIFY are actually deprecated in SECP256K1 and not used in coincurve. Could it bee that CFFI under windows do not include them in the _libsecp256k1.dll?

This test should trigger the fail in our workflow

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (8bfb756) 85.45% compared to head (1dde35a) 85.86%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #134 +/- ## ========================================== + Coverage 85.45% 85.86% +0.40% ========================================== Files 10 11 +1 Lines 557 573 +16 Branches 66 66 ========================================== + Hits 476 492 +16 Misses 45 45 Partials 36 36 ``` | [Files](https://app.codecov.io/gh/ofek/coincurve/pull/134?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev) | Coverage Δ | | |---|---|---| | [coincurve/keys.py](https://app.codecov.io/gh/ofek/coincurve/pull/134?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-Y29pbmN1cnZlL2tleXMucHk=) | `76.76% <100.00%> (ø)` | | | [tests/test\_flags.py](https://app.codecov.io/gh/ofek/coincurve/pull/134?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=Ofek+Lev#diff-dGVzdHMvdGVzdF9mbGFncy5weQ==) | `100.00% <100.00%> (ø)` | |