wininet: Create file with correct file name in test_trailing_slash tests

[Marvin]

Hi,

While running your changed tests on Windows, I think I found new failures.
Being a bot and all I'm not very good at pattern recognition, so I might be
wrong, but could you please double-check?
Full results can be found at
https://testbot.winehq.org/JobDetails.pl?Key=18188

Your paranoid android.


=== w7pro64 (64 bit urlcache) ===
urlcache.c:395: Test failed: GetUrlCacheEntryInfo should have set last error to ERROR_INSUFFICIENT_BUFFER instead of 2
urlcache.c:399: Test failed: GetUrlCacheEntryInfo failed with error 87
urlcache.c:400: Test failed: expected zero ExpireTime
urlcache.c:402: Test failed: expected zero LastModifiedTime
urlcache.c:404: Test failed: expected type NORMAL_CACHE_ENTRY|URLHISTORY_CACHE_ENTRY, got 05000000
urlcache.c:408: Test failed: expected dwExemptDelta 0, got 6292480
urlcache.c:422: Test failed: expected ERROR_INSUFFICIENT_BUFFER, got 2
urlcache.c:426: Test failed: GetUrlCacheEntryInfo failed with error 87
urlcache.c:432: Test failed: expected type NORMAL_CACHE_ENTRY|URLHISTORY_CACHE_ENTRY, got 00000000
urlcache.c:437: Test failed: expected headers size 19, got 6311544
urlcache.c:441: Test failed: HitRate not incremented by one on commit
urlcache.c:448: Test failed: Fileextension isn't unset: xN`
urlcache.c:476: Test failed: RetrieveUrlCacheEntryFile should have set last error to ERROR_INVALID_DATA instead of 2