[ci] Fix linux release forgot to remove old taichi (#2914)

Author: Leonz5288

.github/workflows/release.yml

@@ -50,6 +50,7 @@ jobs:
           export PATH=$LLVM_LIB_ROOT_DIR/bin:/usr/local/cuda/bin:$PATH
           export LLVM_DIR=$LLVM_LIB_ROOT_DIR/lib/cmake/llvm
           export CXX=clang++-8
+          python3 -m pip uninstall taichi -y
           python3 -m pip install --user -r requirements_dev.txt
           python3 -m pip install --user twine
           cd python