[libc] Change the test file names used in readlink_test and readlinka…

…t_test. (llvm#97864)

Attempting to fix the following errors from the build bots:
```
Failed to match LIBC_NAMESPACE::symlink(LINK_VAL, LINK) against Succeeds(0).
Expected return value to be equal to 0 but got -1.
Expected errno to be equal to "Success" but got "File exists".
```

libc/test/src/unistd/readlink_test.cpp

@@ -18,9 +18,9 @@ namespace cpp = LIBC_NAMESPACE::cpp;
 
 TEST(LlvmLibcReadlinkTest, CreateAndUnlink) {
   using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
-  constexpr const char *FILENAME = "readlink_test_value";
+  constexpr const char *FILENAME = "readlink_test_file";
   auto LINK_VAL = libc_make_test_file_path(FILENAME);
-  constexpr const char *FILENAME2 = "readlink.test.link";
+  constexpr const char *FILENAME2 = "readlink_test_file.link";
   auto LINK = libc_make_test_file_path(FILENAME2);
   LIBC_NAMESPACE::libc_errno = 0;
 

libc/test/src/unistd/readlinkat_test.cpp

@@ -20,9 +20,9 @@ namespace cpp = LIBC_NAMESPACE::cpp;
 
 TEST(LlvmLibcReadlinkatTest, CreateAndUnlink) {
   using LIBC_NAMESPACE::testing::ErrnoSetterMatcher::Succeeds;
-  constexpr const char *FILENAME = "readlinkat_test_value";
+  constexpr const char *FILENAME = "readlinkat_test_file";
   auto LINK_VAL = libc_make_test_file_path(FILENAME);
-  constexpr const char *FILENAME2 = "readlinkat.test.link";
+  constexpr const char *FILENAME2 = "readlinkat_test_file.link";
   auto LINK = libc_make_test_file_path(FILENAME2);
   LIBC_NAMESPACE::libc_errno = 0;