[Minor] Remove 'posting in the mailing list' in contributing.md #1201

Job	Run time
test-ubuntu-jemalloc	0s
test-ubuntu-jemalloc-fortify	0s
test-ubuntu-libc-malloc	0s
test-ubuntu-no-malloc-usable-size	0s
test-ubuntu-32bit	0s
test-ubuntu-io-threads	0s
test-ubuntu-reclaim-cache	0s
test-ubuntu-tls	0s
test-ubuntu-tls-no-tls	0s
test-valgrind-misc	0s
test-valgrind-no-malloc-usable-size-misc	0s
test-valgrind-no-malloc-usable-size-test	0s
test-valgrind-test	0s
test-macos-latest	0s
test-macos-latest-cluster	0s
test-macos-latest-sentinel	0s
${{ matrix.name }}	0s
${{ matrix.name }}	0s
${{ matrix.name }}	0s
test-sanitizer-address	0s
test-sanitizer-undefined	0s
build-macos	0s
reply-schemas-validator	0s
test-alpine-jemalloc	0s
test-alpine-libc-malloc	0s
test-freebsd	0s
notify-about-job-results	0s
	0s

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