tests: Improve parse_target_triple warning regex.

Improve the regex, to ensure it only matches against our specific
warning. This should hopefully make it more robust, since
new CMake versions can always introduce new warnings for our
existing code.

test/parse_target_triple/CMakeLists.txt

@@ -2,9 +2,9 @@ corrosion_tests_add_test(parse_target_triple "")
 corrosion_tests_add_test(parse_target_triple_should_fail "")
 
 set_tests_properties("parse_target_triple_build" PROPERTIES FAIL_REGULAR_EXPRESSION
-        "CMake Warning"
+         "CMake Warning at [^\r\n]*FindRust\.cmake:.*(\r)?\n[ \t]*Failed to parse target-triple `"
         )
 
 set_tests_properties("parse_target_triple_should_fail_build" PROPERTIES PASS_REGULAR_EXPRESSION
-    "CMake Warning"
-    )
+         "CMake Warning at [^\r\n]*FindRust\.cmake:.*(\r)?\n[ \t]*Failed to parse target-triple `"
+    )