I was receiving errors trying to get 1.0.3 via jitpack, so I checked piglib on the jitpack site.
Here's the log with the error saying

You are using an outdated version of Java (8). Java 16 or higher is required.

Unfortunately there's no 1.17 full release on either modrinth or curseforge.

Use the Modrinth maven instead if you're still having this issue (I'm assuming you are since the issue isn't closed)

dependencies {
  maven { url = "https://api.modrinth.com/maven" }
}

modApi "maven.modrinth:piglib:1.0.3-1.16"
include "maven.modrinth:piglib:1.0.3-1.16"

I don't know if there was a 1.0.3 release for 1.17, but if not, that'll still need to be uploaded to Modrinth.

With 1.0.3a, there's a new error

java.lang.IllegalArgumentException: Unsupported class file major version 60

Sounds like jitpack doesn't like the a in 1.0.3a?