Update http to https in c#.md #15783

Job	Run time
RPC and mobile compilation check	5m 34s
Sqlc check	5m 3s
check commits	5m 43s
cross compilation	33m 27s
lint code	7m 37s
sample configuration check	3m 26s
run unit tests (btcd unit-cover)	17m 59s
run ubuntu itests (btcd, backend=btcd cover=1)	32m 8s
run windows itest	42m 56s
run unit tests (unit tags="kvdb_etcd")	19m 20s
run ubuntu itests (bitcoind, backend=bitcoind cover=1)	44m 22s
run unit tests (unit tags="kvdb_postgres")	19m 2s
run ubuntu itests (bitcoind-notxindex, backend="bitcoind notxindex")	42m 36s
run unit tests (unit tags="kvdb_sqlite")	17m 18s
run ubuntu itests (bitcoind-rpcpolling, backend="bitcoind rpcpolling" cover=1)	43m 2s
check pinned dependencies (google.golang.org/grpc v1.59.0)	4s
run unit tests (btcd unit-race)	36m 16s
run ubuntu itests (bitcoind-etcd, backend=bitcoind dbbackend=etcd)	56m 0s
check pinned dependencies (github.com/golang/protobuf v1.5.3)	4s
run unit tests (unit-module)	4m 31s
run ubuntu itests (bitcoind-postgres, backend=bitcoind dbbackend=postgres)	1h 20m 2s
run ubuntu itests (bitcoind-sqlite, backend=bitcoind dbbackend=sqlite)	43m 38s
run ubuntu itests (bitcoind-postgres-nativesql, backend=bitcoind dbbackend=postgres nativesql=true)	1h 15m 0s
check release notes updated	5s
run macOS itest	54m 6s
run ubuntu itests (bitcoind-sqlite-nativesql, backend=bitcoind dbbackend=sqlite nativesql=true)	43m 20s
run ubuntu itests (neutrino, backend=neutrino cover=1)	39m 34s
finish	5s
	12h 52m 18s

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