Dropping py2.7, updating to numpy 1.20 as the min tested version #500

Job	Run time
On ubuntu-20.04 with (gcc-7, python-3.9, numpy-1.20)	10m 55s
On ubuntu-20.04 with (gcc-7, python-3.12, numpy-1.20)	1m 13s
On ubuntu-20.04 with (gcc-7, python-3.12, numpy-2.0.1)	11m 6s
On ubuntu-20.04 with (gcc-9, python-3.9, numpy-1.20)	10m 28s
On ubuntu-20.04 with (gcc-9, python-3.12, numpy-1.20)	1m 15s
On ubuntu-20.04 with (gcc-9, python-3.12, numpy-2.0.1)	10m 25s
On macos-latest with (clang, python-3.9, numpy-1.20)	18m 52s
On macos-latest with (clang, python-3.12, numpy-1.20)	1m 10s
On macos-latest with (clang, python-3.12, numpy-2.0.1)	18m 5s
On ubuntu-latest with (gcc-10, python-3.10, numpy-1.23)	10m 2s
On ubuntu-latest with (gcc-11, python-3.10, numpy-1.23)	9m 56s
On ubuntu-latest with (gcc-10, python-3.10, numpy-1.23)	10m 22s
On ubuntu-latest with (gcc-11, python-3.10, numpy-1.23)	10m 6s
On ubuntu-latest with (gcc-10, python-3.11, numpy-1.23)	9m 51s
On ubuntu-latest with (gcc-11, python-3.11, numpy-1.23)	9m 53s
On ubuntu-latest with (gcc-12, python-3.11, numpy-1.23)	10m 1s
On ubuntu-latest with (gcc-10, python-3.11, numpy-1.23)	10m 1s
On ubuntu-latest with (gcc-11, python-3.11, numpy-1.23)	9m 50s
On ubuntu-latest with (gcc-12, python-3.11, numpy-1.23)	10m 1s
	3h 3m 32s

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