ci: add continue-on-error to all cache steps in setup-pgrx composite action

Transient cache-service failures in post-step cleanup were marking the
entire Windows build job as failed even though all actual build work and
artifact uploads had succeeded. This caused the Create GitHub Release job
to be skipped.

Add continue-on-error: true to the Cargo registry, cargo-pgrx binary, and
pgrx home cache steps (the Cargo build artifacts step already had it).
Cache saves are best-effort — a failure only means the next run is slower,
not that the current run should fail.

Author: grove

.github/actions/setup-pgrx/action.yml

@@ -36,6 +36,7 @@ runs:
     # ── Caching ───────────────────────────────────────────────────────────
     - name: Cache Cargo registry
       uses: actions/cache@v5
+      continue-on-error: true  # Transient cache-service failures must not block the build.
       with:
         path: |
           ~/.cargo/registry/index
@@ -58,6 +59,7 @@ runs:
     - name: Cache cargo-pgrx binary
       id: cache-cargo-pgrx
       uses: actions/cache@v5
+      continue-on-error: true  # Transient cache-service failures must not block the build.
       with:
         path: |
           ~/.cargo/bin/cargo-pgrx
@@ -72,6 +74,7 @@ runs:
     - name: Cache pgrx home (~/.pgrx)
       id: cache-pgrx-home
       uses: actions/cache@v5
+      continue-on-error: true  # Transient cache-service failures must not block the build.
       with:
         path: ~/.pgrx
         key: pgrx-home-pg18-pgrx0.18.0-${{ runner.os }}-${{ runner.arch }}