tools: fix code formatter to honor EXCLUDED_PREFIXES when provided a single filename argument without ./ (#17937)
tools: fix code formatter to honor EXCLUDED_PREFIXES when provided a single filename argument without ./ (#17937)

Signed-off-by: John Esmet <b08eaaa5ee85c8ac9f6d8510dacbe3cd211511ab@gmail.com>
lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,lyft/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy,envoyproxy/envoy,envoyproxy/envoy,lyft/envoy