Pin mypy < 1.7 (pydata#8458)

* Pin mypy < 1.7

* ALso 3.9

* restrict CI

Author: dcherian

.github/workflows/ci-additional.yaml

@@ -2,10 +2,10 @@ name: CI Additional
 on:
   push:
     branches:
-      - "*"
+      - "main"
   pull_request:
     branches:
-      - "*"
+      - "main"
   workflow_dispatch: # allows you to trigger manually
 
 concurrency:
@@ -117,7 +117,7 @@ jobs:
           python xarray/util/print_versions.py
       - name: Install mypy
         run: |
-          python -m pip install mypy --force-reinstall
+          python -m pip install "mypy<1.7" --force-reinstall
 
       - name: Run mypy
         run: |
@@ -171,7 +171,7 @@ jobs:
           python xarray/util/print_versions.py
       - name: Install mypy
         run: |
-          python -m pip install mypy --force-reinstall
+          python -m pip install "mypy<1.7" --force-reinstall
 
       - name: Run mypy
         run: |

.github/workflows/ci.yaml

@@ -2,10 +2,10 @@ name: CI
 on:
   push:
     branches:
-      - "*"
+      - "main"
   pull_request:
     branches:
-      - "*"
+      - "main"
   workflow_dispatch: # allows you to trigger manually
 
 concurrency: