CI: Remove corrupted downloads for build retry

[lupyuen]

Summary

We have implemented CI Build Retry for mitigating Download Failures. But right now it will reuse any Corrupted Downloads (instead of deleting them), which will cause CI Build Retry to fail repeatedly: https://github.com/apache/nuttx/actions/runs/24611381081/job/71966407518#step:10:627

Ignored files: system/argtable3/v3.2.0.7402e6e.tar.gz
gzip: stdin: not in gzip format
make[3]: *** [Makefile:76: argtable3] Error 2

This PR proposes to change git clean -fd to git clean -xfdq. This will remove any Corrupted Downloads, preventing their reuse for CI Build Retry:

## Simulate a corrupted download for argtable3
$ tools/configure.sh qemu-armv8a/netnsh
$ Downloading v3.2.0.7402e6e.tar.gz--argtable3
## Press Ctrl-C to stop the build

## `git clean -fd` won't remove the corrupted download 
$ cd ../apps
$ git clean -fd
$ find . -name "v3.2.0.7402e6e.tar.gz" 
./system/argtable3/v3.2.0.7402e6e.tar.gz

## `git clean -xfdq` removes the corrupted download
$ git clean -xfdq 
$ find . -name "v3.2.0.7402e6e.tar.gz" 
## Corrupted download is deleted correctly

git clean -xfdq is also found in the same testbuild script, so we are using it consistently:

nuttx/tools/testbuild.sh

Lines 286 to 291 in 12e8f92

	function distclean {
	echo " Cleaning..."
	if [ -f .config ] || [ -f build/.config ]; then
	if [ ${GITCLEAN} -eq 1 ] || [ ! -z ${cmake} ]; then
	git -C $nuttx clean -xfdq
	git -C $APPSDIR clean -xfdq

Impact

CI Build Retry will now work correctly, retrying any Failed Downloads, instead of reusing them.

Testing

We tested a Normal Build (without errors), since Download Failures are unpredictable and hard to simulate:

• https://github.com/lupyuen18/nuttx/actions/runs/24617084017

We hope to eliminate these Download Errors that we see in NuttX Build Monitor: https://lupyuen.github.io/nuttx-github-jobs/build-monitor

[cederom]

Thank you @lupyuen good catch.. was that causing build problems with my recent PR? :D

[lupyuen]

@cederom All github.com downloads were failing really badly over the past 12 hours, not sure why. Even our NuttX Build Farm was affected, running on my Local PC outside GitHub Actions:

[cederom]

Thank you so much for keeping an eye @lupyuen !! =)