test: Correctly decode UTF-8 literal string paths

Call fs::u8path to convert some UTF-8 string literals to paths, instead
of relying on implicit conversions. The implicit conversions incorrectly
decode const char* paths using the current windows codepage, instead of
treating them as UTF-8. This could cause test failures depending what
environment windows tests are run in.

Issue was reported by MarcoFalke <[email protected]> in
bitcoin/bitcoin#24306 (comment)

Author: ryanofsky

src/test/fs_tests.cpp

@@ -46,8 +46,8 @@ BOOST_AUTO_TEST_CASE(fsbridge_fstream)
 {
     fs::path tmpfolder = m_args.GetDataDirBase();
     // tmpfile1 should be the same as tmpfile2
-    fs::path tmpfile1 = tmpfolder / "fs_tests_₿_🏃";
-    fs::path tmpfile2 = tmpfolder / "fs_tests_₿_🏃";
+    fs::path tmpfile1 = tmpfolder / fs::u8path("fs_tests_₿_🏃");
+    fs::path tmpfile2 = tmpfolder / fs::u8path("fs_tests_₿_🏃");
     {
         std::ofstream file{tmpfile1};
         file << "bitcoin";
@@ -86,7 +86,7 @@ BOOST_AUTO_TEST_CASE(fsbridge_fstream)
     }
     {
         // Join an absolute path and a relative path.
-        fs::path p = fsbridge::AbsPathJoin(tmpfolder, "fs_tests_₿_🏃");
+        fs::path p = fsbridge::AbsPathJoin(tmpfolder, fs::u8path("fs_tests_₿_🏃"));
         BOOST_CHECK(p.is_absolute());
         BOOST_CHECK_EQUAL(tmpfile1, p);
     }