gh-actions: Don't use ubuntu-18 and macos-10.15

There are no longer any gihub actions runners available for these

Note that this means we can't build for ubuntu-18 anymore, but that
should hopefully no longer be relevant, since it's over 5 years old now.

.github/workflows/build-binary-packages.yml

@@ -14,8 +14,8 @@ jobs:
     strategy:
       matrix:
         os:
-        - ubuntu-18.04
         - ubuntu-20.04
+        - ubuntu-22.04
 
     runs-on: ${{ matrix.os }}
 

.github/workflows/build-python-package.yml

@@ -13,7 +13,7 @@ jobs:
     strategy:
       fail-fast: true
       matrix:
-        os: [ubuntu-18.04, macos-10.15]
+        os: [ubuntu-latest, macos-latest]
 
     steps:
     - uses: actions/checkout@v1