chore: upgrade to PF4J 3.8.0 (#2772)

#### What type of PR is this?
/kind improvement
/area core

#### What this PR does / why we need it:
see also https://github.com/pf4j/pf4j/compare/release-3.7.0...release-3.8.0

#### Which issue(s) this PR fixes:

Fixes #2771

#### Special notes for your reviewer:
/cc @halo-dev/sig-halo 
#### Does this PR introduce a user-facing change?

```release-note
升级依赖 PF4J 至 3.8.0
```

build.gradle

@@ -37,7 +37,7 @@ bootJar {
 ext {
     commonsLang3 = "3.12.0"
     base62 = "0.1.3"
-    pf4j = '3.7.0'
+    pf4j = '3.8.0'
     javaDiffUtils = "4.12"
     guava = "31.1-jre"
     jsoup = '1.15.3'