Update swagger-parser to 2.1.15 (#2989)

Updates
[io.swagger.parser.v3:swagger-parser](https://github.com/swagger-api/swagger-parser)
from 2.1.14 to 2.1.15.
[GitHub Release
Notes](https://github.com/swagger-api/swagger-parser/releases/tag/v2.1.15)
- [Version
Diff](swagger-api/swagger-parser@v2.1.14...v2.1.15)


I'll automatically update this PR to resolve conflicts as long as you
don't change it yourself.

If you'd like to skip this version, you can just close this PR. If you
have any feedback, just mention me in the comments below.

Configure Scala Steward for your repository with a
[`.scala-steward.conf`](https://github.com/scala-steward-org/scala-steward/blob/070634501628558e00a7cd623c97bff1995e59e3/docs/repo-specific-configuration.md)
file.

Have a fantastic day writing Scala!

<details>
<summary>Adjust future updates</summary>

Add this to your `.scala-steward.conf` file to ignore future updates of
this dependency:
```
updates.ignore = [ { groupId = "io.swagger.parser.v3", artifactId = "swagger-parser" } ]
```
Or, add this to slow down future updates of this dependency:
```
dependencyOverrides = [{
  pullRequests = { frequency = "30 days" },
  dependency = { groupId = "io.swagger.parser.v3", artifactId = "swagger-parser" }
}]
```
</details>

labels: test-library-update

build.sbt

@@ -692,7 +692,7 @@ lazy val httpCodeGen =
       packExcludeLibJars := Seq("airspec_2.12", "airspec_2.13", "airspec_3"),
       libraryDependencies ++= Seq(
         // Use swagger-parser only for validating YAML format in tests
-        "io.swagger.parser.v3" % "swagger-parser" % "2.1.14" % Test,
+        "io.swagger.parser.v3" % "swagger-parser" % "2.1.15" % Test,
         // Swagger includes dependency to SLF4J, so redirect slf4j logs to airframe-log
         "org.slf4j" % "slf4j-jdk14" % SLF4J_VERSION % Test,
         // For gRPC route scanner test