ci: use DC_SHA1=YesPlease on osx-clang job for CI

7b8cfe34 (Merge branch 'ed/fsmonitor-on-networked-macos', 2022-10-17) broke the build on macOS with sha1dc by bypassing our hash abstraction (git_SHA_CTX etc.), but it wasn't caught before the problematic topic was merged down to the 'master' branch. Nobody was even compile testing with DC_SHA1 set, although it is the recommended choice in these days for folks when they use SHA-1. This was because the default for macOS uses Apple Common Crypto, and both of the two CI jobs did not override the default. Tweak one of them to use DC_SHA1 to improve the coverage. We may want to give similar diversity for Linux jobs so that some of them build with other implementations of SHA-1; they currently all build and test with DC_SHA1 as that is the default on everywhere other than macOS. But let's start small to fill only the immediate need. Signed-off-by: Junio C Hamano <gitster@pobox.com>