src: fix off-thread cert loading in bundled cert mode #1385

Job	Run time
Build slim tarball	1m 42s
x86_64-darwin: with shared libraries	48m 11s
x86_64-linux: with shared libraries	30m 35s
aarch64-darwin: with shared libraries	26m 38s
aarch64-linux: with shared libraries	25m 18s
	2h 12m 24s

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