test: Expect TPM to work on Arch

cockpit-project/bots#7063 adds `swtpm` to our
Arch image, with that TPM functionality now works.

test/machineslib.py

@@ -35,7 +35,7 @@ def hasMonolithicDaemon(image):
 
 # software TPM doesn't work on some OSes
 def hasBrokenTPM(image):
-    return image.startswith("rhel-8") or image == 'arch'
+    return image.startswith("rhel-8")
 
 
 class VirtualMachinesCaseHelpers: