Remove Emacs 26.3 from CI test matrix

### Notes

- Remove emacs_version 26.3 from test matrix
- Keep testing on 27.2, 28.2, and 29.1
- Dependencies now require Emacs 27.1+ (magit and others have updated minimum requirements)

### Testing

This addresses the CI failure where packages required Emacs 27.1 but the workflow
was testing on 26.3. The remaining Emacs versions should be compatible with
current package dependencies.

### Issues
* Fixes Emacs version compatibility issue in GitHub Actions workflow

Author: natsirtguy

.github/workflows/test.yml

@@ -18,7 +18,7 @@ jobs:
     strategy:
       matrix:
         os: [ubuntu-latest]
-        emacs_version: [26.3, 27.2, 28.2, 29.1]
+        emacs_version: [27.2, 28.2, 29.1]
         python-version: [3.8]
 
     steps: