genrule_sandbox_test: Remove space in `}generate` filter

Running `build/soong/tests/genrule_sandbox_test.py pandora_experimental-python-gen-src`
Find Actions with `${m.pandora_experimental-python-gen-src_.moduleDesc}generate${m.pandora_experimental-python-gen-src_.moduleDescSuffix}`
as description that doesn't contains spaces after `}generate`

Test: build/soong/tests/genrule_sandbox_test.py pandora_experimental-python-gen-src
Change-Id: I0f61793be9c602b91984f81f64ba5b4007a3b935