build: use "latest" version of github builders

.github/workflows/packages.yml

@@ -13,7 +13,7 @@ jobs:
           - package_name: psycopg2
           - package_name: psycopg2-binary
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout repos
         uses: actions/checkout@v2
@@ -66,7 +66,7 @@ jobs:
           - {tag: musllinux_1_1, arch: aarch64}
           - {tag: musllinux_1_1, arch: ppc64le}
 
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
     steps:
       - name: Checkout repos
         uses: actions/checkout@v2
@@ -113,7 +113,7 @@ jobs:
 
 
   build-macos:
-    runs-on: macos-10.15
+    runs-on: macos-latest
     strategy:
       fail-fast: false
       matrix:

.github/workflows/tests.yml

@@ -7,7 +7,7 @@ on:
 jobs:
   tests:
     name: Unit tests run
-    runs-on: ubuntu-20.04
+    runs-on: ubuntu-latest
 
     strategy:
       fail-fast: false