fix indentation when printing double cosets (#5841) #5879

Job	Run time
Cross compiler for s390x	27m 24s
Test in OpenBSD	8m 1s
testinstall - - ubuntu-latest	4m 37s
teststandard - - ubuntu-latest	19m 7s
testmanuals - - ubuntu-latest	6m 18s
testexpect testmockpkg testspecial test-compile testlibgap testkernel testworkspace - - ubuntu-latest	6m 44s
testpackages testinstall-loadall - - ubuntu-latest	27m 21s
makemanuals testmakeinstall - CONFIGFLAGS="--prefix=/tmp/gapprefix" NO_COVERAGE=1 - ubuntu-latest	5m 17s
teststandard - ABI=32 CONFIGFLAGS="" - ubuntu-20.04	18m 10s
testinstall - HPCGAP=yes ABI=64 - ubuntu-latest	7m 41s
testmockpkg testinstall - BOOTSTRAP_MINIMAL=yes - macos-latest	4m 15s
testbugfix - CONFIGFLAGS="--enable-memory-checking" - ubuntu-latest	28m 36s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=64 BUILDDIR=out-of-tree CONFIGFLAGS="--enable-valgrind" - ubuntu-latest	4m 31s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=32 BUILDDIR=out-of-tree CONFIGFLAGS="" - ubuntu-20.04	4m 11s
testinstall - JULIA=yes CONFIGFLAGS="--enable-debug" - ubuntu-20.04	4m 42s
testmockpkg testinstall - - windows-2019	15m 14s
Send Slack notification on status change	3s
	3h 12m 12s

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