Import pydriller only for finding bug-introducing commits

To avoid issues in the bug-fixing commits task where git is not installed.

Regression from 7c81a5ece9

.isort.cfg

@@ -4,4 +4,4 @@ include_trailing_comma=True
 force_grid_wrap=0
 use_parentheses=True
 line_length=88
-known_third_party = apispec,apispec_webframeworks,boto3,cerberus,dateutil,flask,flask_cors,hglib,imblearn,joblib,jsone,jsonschema,libmozdata,lmdb,marshmallow,matplotlib,microannotate,models,numpy,orjson,pandas,pkg_resources,pydriller,pyemd,pytest,redis,requests,responses,rq,scipy,setuptools,shap,sklearn,tabulate,taskcluster,tenacity,tqdm,xgboost,yaml,zstandard
+known_third_party = apispec,apispec_webframeworks,boto3,cerberus,dateutil,flask,flask_cors,hglib,imblearn,joblib,jsone,jsonschema,libmozdata,lmdb,marshmallow,matplotlib,microannotate,models,numpy,orjson,pandas,pkg_resources,pyemd,pytest,redis,requests,responses,rq,scipy,setuptools,shap,sklearn,tabulate,taskcluster,tenacity,tqdm,xgboost,yaml,zstandard

scripts/regressor_finder.py

@@ -18,8 +18,6 @@ import tenacity
 from dateutil.relativedelta import relativedelta
 from libmozdata import vcs_map
 from microannotate import utils as microannotate_utils
-from pydriller import GitRepository
-from pydriller.domain.commit import ModificationType
 from tqdm import tqdm
 
 from bugbug import bugzilla, db, repository
@@ -296,6 +294,9 @@ class RegressorFinder(object):
         db.upload(BUG_FIXING_COMMITS_DB)
 
     def find_bug_introducing_commits(self, repo_dir, tokenized):
+        from pydriller import GitRepository
+        from pydriller.domain.commit import ModificationType
+
         logger.info("Download commits to ignore...")
         assert db.download(IGNORED_COMMITS_DB)
         commits_to_ignore = list(db.read(IGNORED_COMMITS_DB))