ci: pass Codecov token as environment variable #36

Job	Run time
reuse	8s
clang-format / Clang-Format	46s
clang-build / Build	38m 33s
message-lint / On Push	16s
message-lint / On Pull Request	0s
secondary-builds (gcc) / Build	35m 30s
secondary-builds (release) / Build	12m 12s
package / Create deb	1m 57s
install / Install	1m 48s
test / Test	10m 5s
package / Create tar	1m 51s
	1h 43m 6s

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