tests: Improve frozen import test coverage.

tests/unix/extra_coverage.py

@@ -60,3 +60,9 @@ from frzstr_pkg2.mod import Foo
 print(Foo.x)
 from frzmpy_pkg2.mod import Foo
 print(Foo.x)
+
+# test raising exception in frozen script
+try:
+    import frzmpy2
+except ZeroDivisionError:
+    print('ZeroDivisionError')

tests/unix/extra_coverage.py.exp

@@ -71,3 +71,4 @@ frzstr_pkg2.mod
 1
 frzmpy_pkg2.mod
 1
+ZeroDivisionError

unix/coverage-frzmpy/frzmpy2.py

+raise ZeroDivisionError