Bump org.spongepowered:mixingradle from 0.7-SNAPSHOT to 0.7.38

Bumps [org.spongepowered:mixingradle](https://github.com/SpongePowered/MixinGradle) from 0.7-SNAPSHOT to 0.7.38.
- [Commits](https://github.com/SpongePowered/MixinGradle/commits)

---
updated-dependencies:
- dependency-name: org.spongepowered:mixingradle
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

build.gradle

@@ -10,7 +10,7 @@ buildscript {
     dependencies {
         classpath "com.github.johnrengelman:shadow:7.1.2"
         classpath "net.minecraftforge.gradle:ForgeGradle:6.+"
-        classpath "org.spongepowered:mixingradle:0.7-SNAPSHOT"
+        classpath "org.spongepowered:mixingradle:0.7.38"
         classpath "xyz.wagyourtail.jvmdowngrader:gradle-plugin:1.0.0"
     }
 }