lint: exclude src/secp256k1 from lint-python-utf8-encoding.sh

It doesn't make sense to use this upstream linter for secp256k1-zkp.
Currently this only affects musig2-vectors.py.

Author: delta1

test/lint/lint-python-utf8-encoding.sh

@@ -9,7 +9,7 @@
 
 export LC_ALL=C
 EXIT_CODE=0
-OUTPUT=$(git grep " open(" -- "*.py" ":(exclude)src/crc32c/" | grep -vE "encoding=.(ascii|utf8|utf-8)." | grep -vE "open\([^,]*, ['\"][^'\"]*b[^'\"]*['\"]")
+OUTPUT=$(git grep " open(" -- "*.py" ":(exclude)src/crc32c/" ":(exclude)src/secp256k1/" | grep -vE "encoding=.(ascii|utf8|utf-8)." | grep -vE "open\([^,]*, ['\"][^'\"]*b[^'\"]*['\"]")
 if [[ ${OUTPUT} != "" ]]; then
     echo "Python's open(...) seems to be used to open text files without explicitly"
     echo "specifying encoding=\"utf8\":"