drotmg.f: Replace GAM**2 by existing GAMSQ #652

Job	Run time
memory-check	11m 11s
coverage	7m 8s
test-install-cblas-lapacke-without-fortran-compiler	5m 11s
test-install-release (macos-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-un...	19m 13s
test-install-release (macos-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-un...	21m 14s
test-install-release (ubuntu-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-u...	9m 19s
test-install-release (ubuntu-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-u...	10m 0s
test-install-release (windows-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-...	14m 16s
test-install-release (windows-latest, -Wall -Wno-unused-dummy-argument -Wno-unused-variable -Wno-...	15m 50s
	1h 53m 22s

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