Add Cbc_modifyCoefficient to C interface. #270

Job	Run time
Run tests (ubuntu-20.04, true, ADD_CXXFLAGS=-fvisibility=hidden, sudo apt install -y -qq gfortran...	7m 39s
Run tests (ubuntu-20.04, false, ADD_CXXFLAGS=-fvisibility=hidden, sudo apt install -y -qq gfortra...	7m 48s
Run tests (ubuntu-22.04, true, ADD_CXXFLAGS=-fvisibility=hidden, sudo apt install -y -qq gfortran...	7m 55s
Run tests (ubuntu-22.04, false, ADD_CXXFLAGS=-fvisibility=hidden, sudo apt install -y -qq gfortra...	7m 52s
Run tests (macos-13, false, CC=clang OSX=13, brew install metis bash)	11m 38s
Run tests (macos-13, false, CC=gcc-13 CXX=g++-13 OSX=13 ADD_CXXFLAGS=-Wl,-ld_classic, brew instal...	12m 37s
Run tests (macos-14, false, CC=gcc-13 CXX=g++-13 OSX=14 ADD_CXXFLAGS=-Wl,-ld_classic, brew instal...	8m 20s
	1h 3m 49s

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