minijinja: build the cp38-abi3 wheel again

The matrix only had a `version` axis, so the two include-only entries
merged into one job and the cp314t entry overwrote cp38-abi3: since
#1937 only the free-threaded wheel was built. Make `tag` a real matrix
axis so each include entry attaches its `build` to its own leg.

Signed-off-by: Ludovic Henry <git@ludovic.dev>

Author: luhenry

.github/workflows/build-minijinja.yml

@@ -50,6 +50,8 @@ jobs:
       fail-fast: false
       matrix:
         version: ${{ fromJSON(needs.setup.outputs.versions) }}
+        # A real axis: include-only entries would merge into one job (gotcha 402).
+        tag: [cp38-abi3, cp314t]
         include:
           # pyo3's abi3-py38 feature is on unconditionally (minijinja-py/Cargo.toml), so
           # one abi3 wheel serves every GIL-ful interpreter; pyo3 disables abi3 under