tests: Skip tests needing machine module if (u)machine doesn't exist.

tests/basics/subclass_native_call.py

@@ -4,13 +4,13 @@
 # and is callable (has call).  The only one available is machine.Signal, which
 # in turns needs PinBase.
 try:
+    try:
         import umachine as machine
-except ImportError:
+    except ImportError:
         import machine
-try:
     machine.PinBase
     machine.Signal
-except AttributeError:
+except:
     print("SKIP")
     raise SystemExit
 

tests/extmod/machine_pinbase.py

@@ -1,10 +1,10 @@
 try:
+    try:
         import umachine as machine
-except ImportError:
+    except ImportError:
         import machine
-try:
     machine.PinBase
-except AttributeError:
+except:
     print("SKIP")
     raise SystemExit
 

tests/extmod/machine_pulse.py

@@ -1,11 +1,11 @@
 try:
+    try:
         import umachine as machine
-except ImportError:
+    except ImportError:
         import machine
-try:
     machine.PinBase
     machine.time_pulse_us
-except AttributeError:
+except:
     print("SKIP")
     raise SystemExit
 

tests/extmod/machine_signal.py

@@ -1,13 +1,13 @@
 # test machine.Signal class
 
 try:
+    try:
         import umachine as machine
-except ImportError:
+    except ImportError:
         import machine
-try:
     machine.PinBase
     machine.Signal
-except AttributeError:
+except:
     print("SKIP")
     raise SystemExit