chore:bump version to 0.12.6 #998

Job	Run time
build-gem	18s
Use gem to package metanorma ubuntu-20.04 Ruby 3.2.6 CC clang-12	17m 17s
Use gem to package metanorma macos-13 Ruby 3.2.6 CC clang	23m 13s
Use gem to package fontist ubuntu-20.04 Ruby 3.2.6 CC clang-12	14m 46s
Use gem to package fontist windows-latest Ruby 3.2.6 CC gcc	56m 29s
Use gem to package metanorma alpine:3.17 Ruby 3.2.6 CC gcc	25m 5s
Use gem to package fontist macos-13 Ruby 3.2.6 CC clang	17m 12s
Use gem to package fontist alpine:3.17 Ruby 3.2.6 CC gcc	22m 16s
Use gem to package metanorma macos-14 Ruby 3.2.6 CC clang	9m 48s
Use gem to package fontist macos-14 Ruby 3.2.6 CC clang	9m 32s
cross-test on ubuntu-22.04	30s
cross-test on ubuntu-24.04	39s
Release gem	0s
	3h 17m 5s

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