Make release_prep.sh executable

Copybara Import from https://github.com/bazelbuild/rules_cc/pull/420

BEGIN_PUBLIC
Make release_prep.sh executable (#420)

Closes #420
END_PUBLIC

COPYBARA_INTEGRATE_REVIEW=https://github.com/bazelbuild/rules_cc/pull/420 from armandomontanez:make-release-script-executable 4583eb019fc50cbb562c01b5812a51b72333701a
PiperOrigin-RevId: 772342190
Change-Id: Ia65c85563350d82401347f21cbca2225160a4aca
diff --git a/.github/workflows/release_prep.sh b/.github/workflows/release_prep.sh
old mode 100644
new mode 100755