[ruby/openssl] Implement FIPS functions on OpenSSL 3.

This commit is to implement the `OpenSSL::OPENSSL_FIPS`, `ossl_fips_mode_get`
and `ossl_fips_mode_set` to pass the test `test/openssl/test_fips.rb`.

It seems that the `OPENSSL_FIPS` macro is not used on the FIPS mode case any
more, and some FIPS related APIs also were removed in OpenSSL 3.

See the document <https://github.com/openssl/openssl/blob/master/doc/man7/migration_guide.pod#removed-fips_mode-and-fips_mode_set>
the section OPENSSL 3.0 > Main Changes from OpenSSL 1.1.1 >
Other notable deprecations and changes - Removed FIPS_mode() and FIPS_mode_set() .

The `OpenSSL::OPENSSL_FIPS` returns always true in OpenSSL 3 because the used
functions `EVP_default_properties_enable_fips` and `EVP_default_properties_is_fips_enabled`
works with the OpenSSL installed without FIPS option.

The `TEST_RUBY_OPENSSL_FIPS_ENABLED` is set on the FIPS mode case on the CI.
Because I want to test that the `OpenSSL.fips_mode` returns the `true` or
'false' surely in the CI. You can test the FIPS mode case by setting
`TEST_RUBY_OPENSSL_FIPS_ENABLED` on local too. Right now I don't find a better
way to get the status of the FIPS mode enabled or disabled for this purpose. I
am afraid of the possibility that the FIPS test case is unintentionally skipped.

I also replaced the ambiguous "returns" with "should return" in the tests.

https://github.com/ruby/openssl/commit/c5b2bc1268

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