Fix failing fn-eval test

e2e/testdata/fn-eval/invalid-fn-config-file/pkg/.expected/config.yaml

@@ -16,4 +16,4 @@ testType: eval
 exitCode: 1
 image: gcr.io/kpt-fn/set-namespace:v0.1.3
 fnConfig: ../../config.yaml
-stdErr: "wrong Node Kind for  expected: MappingNode was ScalarNode: value: {I am not a valid config file}"
+stdErr: "wrong node kind: expected MappingNode but got ScalarNode: node contents:\nI am not a valid config file\n"

pkg/test/runner/util.go

@@ -75,7 +75,9 @@ func gitCommit(d, msg string) error {
 }
 
 func gitDiff(d, commit1, commit2 string) (string, error) {
-	stdout, stderr, err := runCommand(getCommand(d, "git", []string{"diff", commit1, commit2}))
+	command := getCommand(d, "git", []string{"diff", commit1, commit2})
+	command.Env = []string{"GIT_DIFF_OPTS="}
+	stdout, stderr, err := runCommand(command)
 	if err != nil {
 		return "", fmt.Errorf("git diff error: %w, output: %s, stderr: %s", err, stdout, stderr)
 	}