release: 0.3.0 — stamp CEREMONY_SELF_REF in both carriers

release.yml and labels.yml both pin the ref a consumer's run fetches
ceremony at; self-ref-check green against the bumped VERSION.

Refs #160

.github/workflows/labels.yml

@@ -25,7 +25,7 @@ on:
 env:
   # A called workflow arrives without its repository. Keep this literal pin
   # aligned with the ceremony release consumed by callers (issue #9 D3).
-  CEREMONY_SELF_REF: "0.2.0"
+  CEREMONY_SELF_REF: "0.3.0"
 
 jobs:
   scope:

.github/workflows/release.yml

@@ -129,7 +129,7 @@ env:
   # `ref:` accepts ${{ env }}; `uses:` strings do not — which is why the
   # shared logic arrives as script files via checkout, not as inner `uses:`
   # references.
-  CEREMONY_SELF_REF: "0.2.0"
+  CEREMONY_SELF_REF: "0.3.0"
   VERSION_SOURCE: ${{ inputs.version-source }}
 
 jobs: