fix: Extra environment args provided with the run_clusterfuzzlite command where not being used

[4kreed]

Hi there 👋 ,

this is my very first contribution to this project so please let me know if there is anything that I should do differently.

The goal of this small PR is to allow the user that the extra environment arguments that they can provide to the run_clusterfuzzlite command are actually used (before this change the user could provide them but they were not used).

How to reproduce the problem

1. For this example we will be using cifuzz-example, which can be downloaded from https://github.com/jonathanmetzman/cifuzz-example into /path/to/cifuzz-example
2. cd /path/to/cifuzz-example
3. mkdir .clusterfuzzlite
4. cp /path/to/oss-fuzz/projects/cifuzz-example/build.sh .clusterfuzzlite/
5. cp /path/to/oss-fuzz/projects/cifuzz-example/Dockerfile .clusterfuzzlite/
6. Modify .clusterfuzzlite/Dockerfile such that the last line of the file becomes COPY .clusterfuzzlite/build.sh $SRC/ (instead of COPY build.sh $SRC/)
7. Run python3 /path/to/oss-fuzz/infra/helper.py run_clusterfuzzlite --external --branch master -e SANITIZER=coverage /path/to/cifuzz-example

In this scenario you could see that the SANITIZER=coverage environment argument is not being used.

Thanks in advance for your time.

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