Bump org.apache.sling.servlets.post from 2.1.0 to 2.3.8 in /slingbucks

Bumps org.apache.sling.servlets.post from 2.1.0 to 2.3.8.

---
updated-dependencies:
- dependency-name: org.apache.sling:org.apache.sling.servlets.post
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>
diff --git a/slingbucks/pom.xml b/slingbucks/pom.xml
index f9723b4..bf27022 100644
--- a/slingbucks/pom.xml
+++ b/slingbucks/pom.xml
@@ -71,7 +71,7 @@
         <dependency>
             <groupId>org.apache.sling</groupId>
             <artifactId>org.apache.sling.servlets.post</artifactId>
-            <version>2.1.0</version>
+            <version>2.3.8</version>
             <scope>provided</scope>
         </dependency>
         <dependency>