Fix IsCheapConwayPolynomial( p, 1 ) for p < 1000 #4678

Job	Run time
testinstall - - ubuntu-latest	4m 56s
teststandard - - ubuntu-latest	19m 41s
testmanuals - - ubuntu-latest	6m 31s
testexpect testmockpkg testspecial test-compile testlibgap testkernel - - ubuntu-latest	3m 52s
testpackages testinstall-loadall - - ubuntu-latest	21m 51s
makemanuals testmakeinstall - GAPPREFIX=/tmp/gapprefix CONFIGFLAGS="--prefix=/tmp/gapprefix" NO_COVERAGE=1 - ubuntu-latest	5m 38s
teststandard - ABI=32 CONFIGFLAGS="" - ubuntu-20.04	18m 19s
testinstall - HPCGAP=yes ABI=64 - ubuntu-latest	8m 51s
testmockpkg testinstall - BOOTSTRAP_MINIMAL=yes - macos-latest	9m 2s
testbugfix - CONFIGFLAGS="--enable-memory-checking" - ubuntu-latest	20m 54s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=64 BUILDDIR=out-of-tree CONFIGFLAGS="--enable-valgrind" - ubuntu-latest	4m 27s
testbuildsys testmockpkg testinstall - NO_COVERAGE=1 ABI=32 BUILDDIR=out-of-tree CONFIGFLAGS="" - ubuntu-20.04	4m 1s
testinstall - JULIA=yes CONFIGFLAGS="--enable-debug --disable-Werror" - ubuntu-20.04	4m 51s
testmockpkg testinstall - - windows-2019	17m 34s
Send Slack notification on status change	0s
	2h 30m 28s

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