Fix stellar:native asset SEP-38 info validation

[philipliu]

We should be checking asset.asset !== "stellar:native" not asset !== "stellar:native:

❯ yarn stellar-anchor-tests --seps 38 --home-domain http://localhost:8080 --sep-config /Users/philipliu/Documents/work/java-stellar-anchor-sdk/platform/src/test/resources/stellar-anchor-tests-sep-config.json
yarn run v1.22.19
$ node @stellar/anchor-tests/lib/cli.js --seps 38 --home-domain http://localhost:8080 --sep-config /Users/philipliu/Documents/work/java-stellar-anchor-sdk/platform/src/test/resources/stellar-anchor-tests-sep-config.json
✔ SEP-1 › TOML Tests › the TOML file exists at ./well-known/stellar.toml
✔ SEP-38 › TOML Tests › has an ANCHOR_QUOTE_SERVER attribute
failed to read keypair
failed to read keypair
✔ SEP-38 › GET /info › returns a valid info response
✔ SEP-10 › TOML Tests › has a valid WEB_AUTH_ENDPOINT in the TOML file
✔ SEP-10 › POST /auth › returns a valid JWT
✔ SEP-38 › GET /prices › returns a valid response
✔ SEP-38 › GET /prices › allows off-chain assets as 'sell_asset'
✔ SEP-38 › GET /prices › specifying delivery method is optional
✔ SEP-38 › GET /price › returns a valid response with
✔ SEP-38 › GET /price › returned amounts are calculated correctly
✔ SEP-38 › GET /price › accepts the 'buy_amount' parameter with
✔ SEP-38 › GET /price › specifying delivery method is optional with
✔ SEP-38 › POST /quote › requires SEP-10 authentication
✔ SEP-38 › POST /quote › returns a valid response
✔ SEP-38 › POST /quote › quote amounts are correctly calculated
✔ SEP-38 › GET /quote › requires SEP-10 authentication
✔ SEP-38 › GET /quote › can fetch an existing quote
✔ SEP-38 › GET /quote › returns a 404 for unknown quote IDs

Tests:       18 passed, 18 total
Time:        1.571s
✨  Done in 1.92s.

[stellar-jenkins]

Preview is available here:
http://stellar-anchor-tests-pr115.previews.kube001.services.stellar-ops.com/

[stellar-jenkins]

Preview is available here:
http://stellar-anchor-tests-pr115.previews.kube001.services.stellar-ops.com/