workflow: rename all .yml files to .yaml

The original `go.yml` got added via some GH automation. But we
are not MSDOS and we can affort more than 3 chars for a file
extension - so this commit renames all .yml to .yaml which is
what we use everywhere else.

.github/workflows/go.yaml

@@ -13,7 +13,7 @@ jobs:
 
   build:
     runs-on: ubuntu-latest
-    uses:  ./.github/workflows/testdeps.yml
+    uses:  ./.github/workflows/testdeps.yaml
     steps:
     - uses: actions/checkout@v4
 

.github/workflows/pytest.yaml

@@ -9,7 +9,7 @@ on:
 jobs:
   build:
     runs-on: ubuntu-latest
-    uses:  ./.github/workflows/testdeps.yml
+    uses:  ./.github/workflows/testdeps.yaml
     steps:
     - uses: actions/checkout@v4