CI: manually install to prevent incompatible releases

When `pymatgen` gets installed through `pip` it needs to be built and
its build process will not respect any package version requirements that
`aiida-core` imposes. A common problem is that the latest `numpy`
release will get installed, including pre-releases, which often break
our tests because it drops support of certain Python versions.

To workaround this, the workflows are updated to install an explicit
version of `numpy` that we know is compatible before installing
`aiida-core` itself. In this case, `pymatgen` should simply use that
version and not install the latest.

Cherry-pick: c063609

.github/workflows/ci-code.yml

@@ -90,6 +90,13 @@ jobs:
         pip install --upgrade pip
         pip --version
 
+    # Work-around issue caused by pymatgen's setup process, which will install the latest
+    # numpy version (including release candidates) regardless of our actual specification
+    # By installing the version from the requirements file, we should get a compatible version
+    - name: Install numpy
+      run: |
+        pip install `grep 'numpy==' requirements/requirements-py-${{ matrix.python-version }}.txt`
+
     - name: Install aiida-core
       run: |
         pip install --use-feature=2020-resolver -r requirements/requirements-py-${{ matrix.python-version }}.txt

.github/workflows/test-install.yml

@@ -156,6 +156,13 @@ jobs:
 
     - run: pip install --upgrade pip
 
+    # Work-around issue caused by pymatgen's setup process, which will install the latest
+    # numpy version (including release candidates) regardless of our actual specification
+    # By installing the version from the requirements file, we should get a compatible version
+    - name: Install numpy
+      run: |
+        pip install `grep 'numpy==' requirements/requirements-py-${{ matrix.python-version }}.txt`
+
     - name: Install aiida-core
       run: |
         pip install -e .[atomic_tools,docs,notebook,rest,tests]