[hybrid] fix GradientClipByGlobalNorm in hybrid parallel #35691
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huangxu96
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PR types
Bug fixes
PR changes
Others
Describe
修复 #33565 引入的精度bug。
产生原因
上述PR在GradientClipByGlobalNorm里插入了两个sum op，导致混合并行中同样也会插入两个c_allreduce_sum。
原本global_norm = 9 = c_allreduce_sum(5, 4)，增加一个c_allreduce_sum后，global_norm = 18 = c_allreduce_sum(9, 9)，导致出错。
修复方案
临时修复，判断global_norm_var_list的个数，为1则保持原始逻辑只有一个sum。