fix(crypto): migration failure due to optimized handling of &[u8]

[BillCarsonFr]

Fix migration bug caused by #4450 when &[u8] serialization is optimized.

=> Migration bug was causing messages to fail to decrypt and the sync to fail with the following errors

matrix_sdk_crypto::machine: Failed to decrypt a room event: invalid type: byte array, expected a base64 string or an array of 32 bytes

ERROR matrix_sdk::sync: Received an invalid response: failed to read or write to the crypto store invalid type: byte array, expected a base64 string or an array of 32 bytes

• Public API changes documented in changelogs (optional)

Signed-off-by:

[codecov]

Codecov Report

Attention: Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.

Project coverage is 85.36%. Comparing base (7ec384c) to head (1319808).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...x-sdk-crypto/src/olm/group_sessions/sender_data.rs	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4500      +/-   ##
==========================================
- Coverage   85.37%   85.36%   -0.01%     
==========================================
  Files         284      284              
  Lines       31885    31892       +7     
==========================================
+ Hits        27222    27226       +4     
- Misses       4663     4666       +3     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[jmartinesp]

LGTM if I understood the issue correctly 😅 . Left a small comment, and I think we should wait for confirmation from @poljar .

[jmartinesp]

We could use [0u8; Ed25519PublicKey::LENGTH] here too I think, to it's more explicit.

[BillCarsonFr]

Closed. The test was added to the existing PR #4499