Use git grep as opposed to system grep (#7245)
Use git grep as opposed to system grep (#7245)

When running on a system where BSD grep is on the PATH the check fails
because bsd-grep follows symlinks on `grep -r`. This causes the check
to find all the transitive dependencies that are using git on the
`bazel-envoy` symbolic link directory

Signed-off-by: Martin Conte Mac Donell <54669547a225ff20cba8b75a4adca540eef25858@lyft.com>
eklitzke/envoy,eklitzke/envoy,envoyproxy/envoy,jrajahalme/envoy,eklitzke/envoy,jrajahalme/envoy,envoyproxy/envoy,eklitzke/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,jrajahalme/envoy,envoyproxy/envoy-wasm,istio/envoy,lizan/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm,lyft/envoy,lizan/envoy,envoyproxy/envoy-wasm,jrajahalme/envoy,eklitzke/envoy,envoyproxy/envoy,lizan/envoy,jrajahalme/envoy,lizan/envoy,lizan/envoy,istio/envoy,jrajahalme/envoy,istio/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,istio/envoy,istio/envoy,eklitzke/envoy,istio/envoy,lizan/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy-wasm,envoyproxy/envoy-wasm,istio/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy-wasm