python: update some incorrect or obsolete code

* tests/python/ipnbdoctest.py: Use importlib instead of imp.
* tests/python/ltlparse.py: Fix invalid escape sequence.

tests/python/ipnbdoctest.py

@@ -22,9 +22,9 @@ except ImportError:
     print('Python 3.x is needed to run this script.')
     sys.exit(77)
 
-import imp
+import importlib
 try:
-    imp.find_module('IPython')
+    importlib.util.find_spec('IPython')
 except:
     print('IPython is needed to run this script.')
     sys.exit(77)

tests/python/ltlparse.py

@@ -25,7 +25,7 @@ import spot
 
 e = spot.default_environment.instance()
 
-l = ['GFa', 'a U (((b)) xor c)', '!(FFx <=> Fx)', 'a \/ a \/ b \/ a \/ a'];
+l = ['GFa', 'a U (((b)) xor c)', '!(FFx <=> Fx)', 'a \\/ a \\/ b \\/ a \\/ a']
 
 for str1 in l:
     pf = spot.parse_infix_psl(str1, e, False)