RFR: 8371573: Shenandoah: Fix style of include directive

[Kelvin Nilsen]

Fix style of include directive for improved consistency and compatibility with GraalVM conventions.

-------------

Commit messages:
 - Fix style of include directive

Changes: https://git.openjdk.org/jdk/pull/28219/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28219&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371573
  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28219.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28219/head:pull/28219

PR: https://git.openjdk.org/jdk/pull/28219