Fix Java version for gradle:7.4.2.

When Gradle version was bumped to 7.0.0, it required Java version 11.
In 82b9121 (2022/01/05), .sdkmanrc was adjusted to accommodate.  But
app/build.gradle.kts was not.

More recent Gradle releases have started to complain:
,----
| > Could not resolve all files for configuration ':classpath'.
|    > Could not resolve com.android.tools.build:gradle:7.4.2.
|      Required by:
|          project :
|       > No matching variant of com.android.tools.build:gradle:7.4.2 was found. The consumer was configured to find a library for use during runtime, compatible with Java 8, packaged as a jar, and its dependencies declared externally, as well as attribute 'org.gradle.plugin
| .api-version' with value '8.0.2' but:
|           - Variant 'apiElements' capability com.android.tools.build:gradle:7.4.2 declares a library, packaged as a jar, and its dependencies declared externally:
|               - Incompatible because this component declares a component for use during compile-time, compatible with Java 11 and the consumer needed a component for use during runtime, compatible with Java 8
|               - Other compatible attribute:
|                   - Doesn't say anything about org.gradle.plugin.api-version (required '8.0.2')
`----

Adjust gradle’s specification to suit.

app/build.gradle.kts

@@ -35,8 +35,8 @@ androidGitVersion {
 
 android {
   compileOptions {
-    sourceCompatibility = JavaVersion.VERSION_1_8
-    targetCompatibility = JavaVersion.VERSION_1_8
+    sourceCompatibility = JavaVersion.VERSION_11
+    targetCompatibility = JavaVersion.VERSION_11
   }
 
   namespace = "audio.funkwhale.ffa"
@@ -46,7 +46,7 @@ android {
   }
 
   kotlinOptions {
-    jvmTarget = JavaVersion.VERSION_1_8.toString()
+    jvmTarget = JavaVersion.VERSION_11.toString()
   }
 
   buildFeatures {