Allow skipping redirects for extensions. #405

Job	Run time
cs-stan / Coding Standard & Static Analysis	23s
testsuite / testsuite-linux (8.1, highest, false)	21s
testsuite / testsuite-linux (8.1, lowest, false)	17s
testsuite / testsuite-linux (8.3, highest, false)	18s
testsuite / testsuite-linux (8.2, highest, false)	17s
testsuite / testsuite-linux (8.4, highest, false)	19s
	1m 55s

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