test: don't use `-cpu max` in GH Actions

There appears to be an issue with newer QEMU versions (spotted with Arch
Linux and C9S containers) which causes the respective GH Action to hang
when booting a QEMU VM in combination with the `-cpu max` parameter.

During (a particularly painful) debugging session I once managed to get
some output from such "frozen" machine (using `earlycon` and
`earlyprintk` kernel cmdline options), and in that particular case the
VM died with a trap caused by an invalid opcode.

I couldn't reproduce this locally, only in GH Actions environment with
Arch Linux and C9S containers. Also, so far I haven't found out which
specific CPUID flag causes this, but using the `IvyBridge-v2` feature
set seems to mitigate the issue.

test/run-qemu

@@ -3,13 +3,14 @@
 # We prefer kvm, kqemu, userspace in that order.
 
 export PATH=/usr/sbin:/usr/bin:/sbin:/bin
+QEMU_CPU="${QEMU_CPU:-max}"
 
-[[ -x /usr/bin/qemu ]] && BIN=/usr/bin/qemu && ARGS=(-cpu max)
+[[ -x /usr/bin/qemu ]] && BIN=/usr/bin/qemu && ARGS=(-cpu "$QEMU_CPU")
 (lsmod | grep -q '^kqemu ') && BIN=/usr/bin/qemu && ARGS=(-kernel-kqemu -cpu host)
 [[ -c /dev/kvm && -x /usr/bin/kvm ]] && BIN=/usr/bin/kvm && ARGS=(-cpu host)
 [[ -c /dev/kvm && -x /usr/bin/qemu-kvm ]] && BIN=/usr/bin/qemu-kvm && ARGS=(-cpu host)
 [[ -c /dev/kvm && -x /usr/libexec/qemu-kvm ]] && BIN=/usr/libexec/qemu-kvm && ARGS=(-cpu host)
-[[ -x /usr/bin/qemu-system-$(uname -m) ]] && BIN=/usr/bin/qemu-system-$(uname -m) && ARGS=(-cpu max)
+[[ -x /usr/bin/qemu-system-$(uname -m) ]] && BIN=/usr/bin/qemu-system-$(uname -m) && ARGS=(-cpu "$QEMU_CPU")
 [[ -c /dev/kvm && -x /usr/bin/qemu-system-$(uname -m) ]] && BIN=/usr/bin/qemu-system-$(uname -m) && ARGS=(-enable-kvm -cpu host)
 
 [[ $BIN ]] || {

tools/test-github.sh

@@ -41,6 +41,7 @@ else
             cd /lib/modules
             ls -1 | tail -1
         )" \
+        QEMU_CPU="IvyBridge-v2" \
         DRACUT_NO_XATTR=1 \
         TEST_RUN_ID="$RUN_ID" \
         ${TESTS:+TESTS="$TESTS"} \