community/mtxclient: fails on 3.15 builders

fails on few arches

[ 10%] Building CXX object CMakeFiles/matrix_client.dir/lib/structs/errors.cpp.o
[01m[K/home/buildozer/aports/community/mtxclient/src/mtxclient-0.5.1/lib/crypto/client.cpp:40:1:[m[K [01;31m[Kerror: [m[Kreference to '[01m[KOlmErrorCode[m[K' is ambiguous
   40 | [01;31m[KOlmErrorCode[m[K
      | [01;31m[K^~~~~~~~~~~~[m[K
In file included from [01m[K/home/buildozer/aports/community/mtxclient/src/mtxclient-0.5.1/lib/crypto/client.cpp:8[m[K:
[01m[K/home/buildozer/aports/community/mtxclient/src/mtxclient-0.5.1/include/mtxclient/crypto/client.hpp:34:12:[m[K [01;36m[Knote: [m[Kcandidates are: '[01m[Kenum class mtx::crypto::OlmErrorCode[m[K'

Edited Oct 24, 2021 by Andy Postnikov

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