work around libgit2 randomly changing the constness of arguments to g… #1590

Job	Run time
stylecheck	19s
build-pr-review	3m 41s
build (ubuntu:focal, g++, gcc, all)	15m 41s
build-arch (all)	15m 39s
build (ubuntu:focal, g++, gcc, horizon.so)	4m 58s
build-debug	14m 50s
build-arch (horizon.so)	4m 38s
build-opensuse (all)	14m 25s
build (ubuntu:jammy, g++, gcc, all)	12m 47s
build-opensuse (horizon.so)	5m 42s
build (ubuntu:jammy, g++, gcc, horizon.so)	4m 13s
build (ubuntu:noble, g++, gcc, all)	15m 16s
build (ubuntu:noble, g++, gcc, horizon.so)	4m 43s
build (debian:bullseye, g++, gcc, all)	13m 5s
build (debian:bullseye, g++, gcc, horizon.so)	4m 23s
build (debian:bookworm, clang, clang, all)	13m 45s
build (debian:bookworm, clang, clang, horizon.so)	4m 22s
build (debian:bookworm, g++, gcc, all)	14m 58s
build (debian:bookworm, g++, gcc, horizon.so)	4m 45s
	2h 52m 10s

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