chore: bump com.guardsquare:proguard-gradle from 7.3.0 to 7.8.1

Bumps [com.guardsquare:proguard-gradle](https://github.com/Guardsquare/proguard) from 7.3.0 to 7.8.1.
- [Release notes](https://github.com/Guardsquare/proguard/releases)
- [Commits](Guardsquare/proguard@v7.3.0...v7.8.1)

---
updated-dependencies:
- dependency-name: com.guardsquare:proguard-gradle
  dependency-version: 7.8.1
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]

tooling/custom-lint-rules/build.gradle

@@ -18,7 +18,7 @@ buildscript {
     dependencies {
         classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
         classpath "com.android.tools.build:gradle:$gradle_version"
-        classpath 'com.guardsquare:proguard-gradle:7.3.0'
+        classpath 'com.guardsquare:proguard-gradle:7.8.1'
     }
 }