util/cache_test: Unset env vars left after Cache.List test

The environment variables are persistent and must be explicitly unset by
each cache test, otherwise next test will fail. Add the missing unsets to
the Cache.List test.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/20256>

src/util/tests/cache_test.cpp

@@ -1165,6 +1165,9 @@ TEST_F(Cache, List)
 
    int err = rmrf_local(CACHE_TEST_TMP);
    EXPECT_EQ(err, 0) << "Removing " CACHE_TEST_TMP " again";
+
+   unsetenv("MESA_DISK_CACHE_SINGLE_FILE");
+   unsetenv("MESA_DISK_CACHE_READ_ONLY_FOZ_DBS_DYNAMIC_LIST");
 #endif /* FOZ_DB_UTIL_DYNAMIC_LIST */
 #endif /* ENABLE_SHADER_CACHE */
 }