lib: fix sequence argument handling in Blob constructor #4108

Job	Run time
Build slim tarball	1m 42s
aarch64-linux: with shared libraries	20m 12s
x86_64-linux: with shared libraries	23m 5s
aarch64-darwin: with shared libraries	20m 43s
x86_64-darwin: with shared libraries	33m 13s
	1h 38m 55s

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