build: workaround for an actions/checkout bug

a9a6e9e and ea43df2 removed a step that was probably intended to
work around actions/checkout#290 and
actions/checkout#882, but broke the CI build
if anyone used a lightweight tag (because these fetch lines actually
shallow the tag depth to 1). This commit attempts to thread the needle
by making this workaround conditional only to releases, where (if the
person doing the release has followed the steps correctly), there is
guaranteed to be an annotated tag at depth 1 in the tag history. (If I'm
parsing the checkout bugs correctly, they only trigger on a tag action
anyways.)

.github/workflows/ci.yml

@@ -292,6 +292,9 @@ jobs:
       - uses: actions/checkout@v3
         with:
           fetch-depth: 0 # all history
+      - name: Fix tags for release # work around https://github.com/actions/checkout/issues/882
+        if: github.event.release.tag_name != null
+        run: git fetch --depth=1 origin +refs/tags/*:refs/tags/* # will break on a lightweight tag
       - name: Checkout submodules
         shell: bash
         run: |