Need to close connection when done uploading via httr::VERB()

[juliasilge]

Maybe related to #333?

If you use httr::VERB(), there are some lingering open connections after uploading a file:

citation <- httr::upload_file(system.file("CITATION"))
httr::VERB(
  "POST",
  url =  "http://httpbin.org/post",
  body = citation
)
#> Response [http://httpbin.org/post]
#>   Date: 2025-04-26 01:24
#>   Status: 200
#>   Content-Type: application/json
#>   Size: 1.19 kB
#> {
#>   "args": {}, 
#>   "data": "bibentry(\"Manual\",\n         title = \"R: A Language and Environ...
#>   "files": {}, 
#>   "form": {}, 
#>   "headers": {
#>     "Accept": "application/json, text/xml, application/xml, */*", 
#>     "Accept-Encoding": "deflate, gzip", 
#>     "Content-Length": "643", 
#>     "Content-Type": "text/plain", 
#> ...
showConnections()
#>   description                                                                         
#> 3 ""                                                                                  
#> 4 "/Library/Frameworks/R.framework/Versions/4.5-arm64/Resources/library/base/CITATION"
#>   class  mode  text     isopen   can read can write
#> 3 "file" "w+b" "binary" "opened" "yes"    "yes"    
#> 4 "file" "rb"  "binary" "opened" "yes"    "no"

^{Created on 2025-04-25 with reprex v2.1.1}

This is showing up in pins on Connect pretty dramatically (you'll see a half dozen "closing unused connection" if you write and then read a pin to Connect), as well as (I believe) other pins backends like GCS.