subp_of_interest: fix regexp escaping

Escape filenames before including them in regexps: on Windows, these
contain backslashes, which have special interpretations. In the general
case, these filenames also contain dots, which mean "any character"
whereas in this context we meant "a dot".

Author: pmderodat

testsuite/tests/subp_of_interest/test.py

@@ -6,6 +6,7 @@
 
 import os
 import os.path
+import re
 
 from SCOV.minicheck import build_and_run, check_xcov_reports
 from SUITE.context import thistest
@@ -151,8 +152,8 @@ def check_xcov(label, args, expected_output=""):
     thistest.fail_if_no_match(
         what="unexpected coverage output",
         regexp=(
-            f".*Error when parsing --subprograms argument {pkg_body}:14:"
-            " unknown subprogram"
+            ".*Error when parsing --subprograms argument"
+            f" {re.escape(pkg_body)}:14: unknown subprogram"
         ),
         actual=contents_of("xcov-wrong3.txt"),
     )