CI: fix the GitHub Actions trigger in docker.yml (numpy#18912)

Also remove `tags: *`, this is unnecessary. This mirrors the
fix in SciPy, so should work. Somehow GitHub Actions no longer
likes `./` at the start of a path.

.github/workflows/docker.yml

@@ -5,10 +5,8 @@ on:
     branches:
       - main
     paths:
-      - './environment.yml'
-    tags:
-      - '*'
-
+      - 'environment.yml'
+
 jobs: 
   build:
     name: Build base Docker image 
@@ -56,4 +54,4 @@ jobs:
             numpy/numpy-dev:${{ steps.getrefs.outputs.date }}-${{ steps.getrefs.outputs.branch}}-${{ steps.getrefs.outputs.sha8 }}, numpy/numpy-dev:latest
       - name: Image digest 
         # Return details of the image build: sha and shell
-        run: echo ${{ steps.docker_build.outputs.digest }}
+        run: echo ${{ steps.docker_build.outputs.digest }}

environment.yml

@@ -1,6 +1,8 @@
 # To use:
+#
 #   $ conda env create -f environment.yml  # `mamba` works too for this command
 #   $ conda activate numpy-dev
+#
 name: numpy-dev
 channels:
   - conda-forge