Bump mongo from 5.0.20 to 5.0.21 in /test/IntegrationTests/docker #7233

Job	Run time
build / build (windows-2022, /c/ProgramData/OpenTelemetry .NET AutoInstrumentation/logs)	7m 27s
build / build (ubuntu-20.04, /var/log/opentelemetry/dotnet)	5m 22s
build-container / build-container (alpine, linux-musl)	5m 57s
build / build (macos-11, /var/log/opentelemetry/dotnet)	9m 8s
build-container / build-container (centos, linux-glibc)	6m 19s
test-build-container (alpine, alpine, linux-musl)	13m 47s
test-build-container (centos, centos, linux-glibc)	14m 37s
test-build-container (debian, centos, linux-glibc)	12m 25s
test-build-native (windows-2022)	7m 41s
test-build-managed (net7.0, windows-2022)	19m 18s
test-build-windows-container-tests (windows-2022, windows-only)	19m 23s
test-build-managed (net7.0, ubuntu-20.04)	9m 48s
test-build-managed (net7.0, macos-11)	14m 17s
test-build-managed (net6.0, windows-2022)	18m 4s
test-build-managed (net6.0, ubuntu-20.04)	10m 45s
test-build-managed (net6.0, macos-11)	13m 2s
test-build-managed (net462, windows-2022)	17m 3s
build-nuget-packages / build-nuget-packages	5m 6s
test-nuget-packages (ubuntu-20.04)	3m 22s
test-nuget-packages (macos-11)	7m 12s
test-nuget-packages (windows-2022)	6m 7s
	3h 46m 10s

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