Duplicated feed logs when having multiple feeds

[StasDeep]

Description

When I have multiple feeds and a blocking feed storage, I get duplicated feed logs.

Steps to Reproduce

1. Create a test.py file with this spider and settings
2. scrapy runspider test.py -L INFO

Expected behavior:

2020-06-09 19:23:03 [scrapy.extensions.feedexport] INFO: Stored json feed (10 items) in: gs://bucket/output.json
2020-06-09 19:23:03 [scrapy.extensions.feedexport] INFO: Stored csv feed (10 items) in: gs://bucket/output.csv

Actual behavior:

2020-06-09 19:23:03 [scrapy.extensions.feedexport] INFO: Stored csv feed (10 items) in: gs://bucket/output.csv
2020-06-09 19:23:03 [scrapy.extensions.feedexport] INFO: Stored csv feed (10 items) in: gs://bucket/output.csv

Versions

Scrapy       : 2.1.0
lxml         : 4.5.1.0
libxml2      : 2.9.10
cssselect    : 1.1.0
parsel       : 1.6.0
w3lib        : 1.22.0
Twisted      : 20.3.0
Python       : 3.7.4 (default, Sep  4 2019, 15:20:53) - [Clang 10.0.0 (clang-1000.10.44.4)]
pyOpenSSL    : 19.1.0 (OpenSSL 1.1.1g  21 Apr 2020)
cryptography : 2.9.2
Platform     : Darwin-19.4.0-x86_64-i386-64bit

Additional context

We use custom GoogleCloudFeedStorage and it takes some time to store the data. While it's doing uploading, next iteration of a for loop inside FeedExporter.close_spider comes and creates new log_args object, although the last one is used in closure.

[StasDeep]

I think I can create a PR fixing that.