[Tests] Fix test_gui_fileuploader failing

[troopa81]

Description

test_gui_fileuploader is failing very often recently and disturb CI. See here for instance

FAIL! : TestQgsFileUploader::testSslError(self-signed) Compared values are not the same
Actual (mErrorMessage): "Upload failed: Connection closed"
Expected (result) : "Upload failed: SSL handshake failed: The certificate is self-signed, and untrusted"

I assume this is related to the online service not responding correctly and closing the connection.

I propose to use a local badssl server instead of a remote one.

AI tool usage

• Claude helped me to setup the nginx/openssl configuration

[nyalldawson]

Thanks @troopa81 , this is a much needed cleanup!

There's a few other tests which also call out to badssl (eg network access manager ones) could those also be flipped over?

[troopa81]

There's a few other tests which also call out to badssl (eg network access manager ones) could those also be flipped over?

Done for all tests that were using badssl.com . Those tests were disabled in CI, so I re-enabled them except testSslErrorHandler in testqgsnetworkmanager.cpp which blocks 90% of the time.

[github-actions]

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
To execute locally, unzip the downloaded zip file and run bin\qgis-bin.exe in the extracted directory.
You might be prompted by Windows Defender click "Run anyway"
(Built from commit 6b4752c)

🍎 MacOS Qt6 builds

Download MacOS Qt6 builds of this PR for testing.
This app is not notarized, run sudo xattr -d com.apple.quarantine /Applications/QGIS*.app to avoid the warning
(Built from commit 6b4752c)