Fix deadlock when shuting down http client. (#2337) #8574

Job	Run time
CMake test (with abseil)	8m 27s
CMake clang 14 (maintainer mode, async)	18m 29s
CMake clang 14 (maintainer mode, sync)	17m 42s
CMake gcc 12 (maintainer mode, async)	16m 1s
CMake gcc 12 (maintainer mode, C++11, async)	11m 24s
CMake gcc 12 (maintainer mode, sync)	12m 11s
CMake msvc (maintainer mode)	14m 6s
CMake test (without otlp-exporter)	6m 58s
CMake test (with opentracing-shim)	6m 31s
CMake test (without otlp-exporter and with async export)	9m 52s
Bazel noexcept	21m 45s
Bazel nortti	21m 18s
Bazel	23m 32s
Bazel with async export	28m 44s
Bazel valgrind	23m 25s
Bazel with external abseil	21m 11s
CMake do not install test (with otlp-exporter)	22m 5s
CMake gcc 4.8 (without otlp exporter)	6m 23s
CMake gcc 4.8 (with otlp exporter)	15m 1s
CMake install test (with abseil)	6m 31s
CMake test (with modern protobuf,grpc and abseil)	28m 51s
CMake test (build shared libraries with otlp-exporter and static gRPC)	20m 23s
CMake test (with otlp-exporter)	20m 54s
CMake C++20 test(Clang with libc++)	11m 25s
CMake C++20 test(GCC)	12m 26s
Plugin -> CMake	1m 36s
Bazel asan config	13m 43s
Bazel tsan config	21m 45s
Bazel on MacOS	23m 9s
Benchmark	13m 7s
Code coverage	19m 52s
DocFX check	43s
Copyright	7s
Format	26s
markdown-lint	1m 16s
misspell	9s
CMake -> exporter proto	16m 48s
Bazel Windows	33m 59s
Plugin -> CMake Windows	12m 22s
CMake (With async export) -> exporter proto	19m 55s
CMake -> exporter proto (Build as DLL)	17m 32s
	10h 2m 4s

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