tmpl: add escape for `@` using `@@` #6975

Job	Run time
tests-sanitize-address-clang	2h 2m 36s
tests-sanitize-address-gcc	2h 32m 0s
tests-sanitize-address-msvc	4m 48s
tests-sanitize-memory-clang	3h 12m 18s
tests-sanitize-undefined-clang	57m 38s
tests-sanitize-undefined-gcc	1h 29m 52s
	10h 19m 12s

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