lib: fix sequence argument handling in Blob constructor #4103

Job	Run time
Build slim tarball	2m 16s
aarch64-linux: with shared libraries	17m 24s
aarch64-darwin: with shared libraries	19m 34s
x86_64-darwin: with shared libraries	19m 41s
x86_64-linux: with shared libraries	19m 26s
	1h 18m 21s

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