Merge pull request #2191 from rburing/gr_poly_scalar_mul #3023

Job	Run time
GCC build regression check (no tests)	1m 3s
macOS-M1, Clang (x3)	8m 16s
Ubuntu GCC, Code Coverage (x10)	30m 0s
Ubuntu GCC with NTL (assert, x2)	8m 54s
Alpine Linux, musl, 32-bit (assert, x1.5)	14m 1s
MinGW GCC (x0.5)	11m 12s
MSVC (x1)	10m 4s
Ubuntu Clang, BLAS and examples (x5)	14m 4s
Nemo.jl	5m 49s
	1h 43m 23s

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