Use \" instead of ' for exiv2 command string

The original failed on some Windows test runs.

Author: jim-easterbrook

tests/bugfixes/github/test_pr_1999.py

@@ -1,28 +1,28 @@
-# -*- coding: utf-8 -*-
-
-import system_tests
-from system_tests import CaseMeta, path
-
-class TestXmpDateTimeSetting(metaclass=CaseMeta):
-    """
-    Test fix for issue 1998.
-    """
-
-    infile = path("$data_path/issue_1998.xmp")
-    commands = [
-        "$exiv2 -M'set Xmp.xmp.CreateDate XmpText 2021-02-03T12:00:00+01:00' $infile",
-        "$exiv2 -K Xmp.xmp.CreateDate $infile",
-        "$exiv2 -M'set Xmp.xmp.CreateDate XmpText 2021-02-03T12:34:56+02:00' $infile",
-        "$exiv2 -K Xmp.xmp.CreateDate $infile",
-        ]
-    stdout = [
-        """""",
-        """Xmp.xmp.CreateDate                           XmpText    25  2021-02-03T12:00:00+01:00
-""",
-        """""",
-        """Xmp.xmp.CreateDate                           XmpText    25  2021-02-03T12:34:56+02:00
-""",
-              ]
-    stderr = [""]*4
-    retval = [0]*4
-
+# -*- coding: utf-8 -*-
+
+import system_tests
+from system_tests import CaseMeta, path
+
+class TestXmpDateTimeSetting(metaclass=CaseMeta):
+    """
+    Test fix for issue 1998.
+    """
+
+    infile = path("$data_path/issue_1998.xmp")
+    commands = [
+        "$exiv2 -M\"set Xmp.xmp.CreateDate XmpText 2021-02-03T12:00:00+01:00\" $infile",
+        "$exiv2 -K Xmp.xmp.CreateDate $infile",
+        "$exiv2 -M\"set Xmp.xmp.CreateDate XmpText 2021-02-03T12:34:56+02:00\" $infile",
+        "$exiv2 -K Xmp.xmp.CreateDate $infile",
+        ]
+    stdout = [
+        "",
+        """Xmp.xmp.CreateDate                           XmpText    25  2021-02-03T12:00:00+01:00
+""",
+        "",
+        """Xmp.xmp.CreateDate                           XmpText    25  2021-02-03T12:34:56+02:00
+""",
+              ]
+    stderr = [""]*4
+    retval = [0]*4
+