release: resolve next *untagged* patch version

The stable-phase version resolver did a single patch bump from VersionPrefix
(1.0.0 -> 1.0.1), so every release after the first collided: the 1.0.2 release
attempt re-resolved 1.0.1 and PSGallery rejected it (409, already exists).
Loop the patch bump until the candidate tag is free. Verified locally: with
v1.0.0 and v1.0.1 present, resolves 1.0.2.

Author: tig

.github/workflows/release.yml

@@ -122,10 +122,12 @@ jobs:
             $full = "$prefix-$pre"
           }
           else {
-            # Stable phase: bump patch if this exact version was already tagged.
+            # Stable phase: start at the prefix and bump the patch until we find
+            # a version that isn't already tagged (so successive releases off the
+            # same VersionPrefix don't collide with an already-published patch).
             $base = $prefix; $pre = ''
-            if (git tag --list "v$prefix") {
-              $p = $prefix -split '\.'
+            while (git tag --list "v$base") {
+              $p = $base -split '\.'
               $p[2] = [string]([int]$p[2] + 1)
               $base = $p -join '.'
             }