Update maturin upper bound to < 1.3

This raises the upper version bound to 1.3.

The package was built and tested with each latest minor version of
maturin since 0.14 (0.15.3, 1.0.1, 1.1.0 and 1.2.3) by incrementally
increasing the upper bound and running :

```
# edit version then :
pip install --verbose --no-binary :all: . && pytest
```

https://www.maturin.rs/changelog

.github/workflows/tag.yml

@@ -48,7 +48,7 @@ jobs:
           profile: minimal
       - name: install maturin
         # Keep the Maturin version in sync with pyproject.toml.
-        run: pip install "maturin>=0.14,<0.15"
+        run: pip install "maturin>=0.14,<1.3"
         # On Linux we'll run Maturin in a Docker container.
         if: matrix.platform.os != 'ubuntu-latest'
       - name: build wheel

pyproject.toml

@@ -1,4 +1,4 @@
 [build-system]
 # Keep the Maturin version in sync with tag.yml.
-requires = ["maturin>=0.14,<0.15"]
+requires = ["maturin>=0.14,<1.3"]
 build-backend = "maturin"