Bump flexmark from 0.62.2 to 0.64.0 (#8621)

Bumps [flexmark](https://github.com/vsch/flexmark-java) from 0.62.2 to 0.64.0.
- [Release notes](https://github.com/vsch/flexmark-java/releases)
- [Commits](vsch/flexmark-java@0.62.2...0.64.0)

---
updated-dependencies:
- dependency-name: com.vladsch.flexmark:flexmark
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

build.gradle

@@ -194,7 +194,7 @@ dependencies {
         exclude module: "log4j-core"
     }
 
-    implementation 'com.vladsch.flexmark:flexmark:0.62.2'
+    implementation 'com.vladsch.flexmark:flexmark:0.64.0'
     implementation 'com.vladsch.flexmark:flexmark-ext-gfm-strikethrough:0.64.0'
     implementation 'com.vladsch.flexmark:flexmark-ext-gfm-tasklist:0.64.0'