GPUUploadManager: wait for running updates to exit in the dtor #4152

Job	Run time
Linux -> Pre-checks	18s
Linux -> Clang-NO_GLSLANG-x64, Debug	8m 31s
Linux -> GCC-x64, Debug	11m 54s
Linux -> Clang-x64, Release	13m 40s
Linux -> GCC-x64, Release	10m 35s
Linux -> Clang-NO_GLSLANG-NO_HLSL-x64, Release	6m 39s
Linux -> Clang-x64, Debug	13m 11s
Linux -> Pre-checks	18s
Linux -> GCC-x64, Release	10m 31s
Linux -> Clang-x64, Debug	13m 11s
Linux -> Clang-NO_GLSLANG-x64, Debug	8m 31s
Linux -> GCC-x64, Debug	11m 54s
Linux -> Clang-x64, Release	13m 40s
Linux -> Clang-NO_GLSLANG-NO_HLSL-x64, Release	6m 39s
	2h 9m 32s

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