DOC: Update action commit SHA to the 0.6.0 tag (#94)

* For stability provide the commit SHA that corresponds to the 0.6.0
  tag for users to pin to.

Author: matthewfeickert

README.md

@@ -12,7 +12,7 @@ jobs:
   steps:
     ...
     - name: Upload wheel
-      uses: scientific-python/upload-nightly-action@b67d7fcc0396e1128a474d1ab2b48aa94680f9fc # 0.5.0
+      uses: scientific-python/upload-nightly-action@ccf29c805b5d0c1dc31fa97fcdb962be074cade3 # 0.6.0
       with:
         artifacts_path: dist
         anaconda_nightly_upload_token: ${{secrets.UPLOAD_TOKEN}}
@@ -57,7 +57,7 @@ jobs:
   steps:
     ...
     - name: Upload wheel
-      uses: scientific-python/upload-nightly-action@b67d7fcc0396e1128a474d1ab2b48aa94680f9fc # 0.5.0
+      uses: scientific-python/upload-nightly-action@ccf29c805b5d0c1dc31fa97fcdb962be074cade3 # 0.6.0
       with:
         artifacts_path: dist
         anaconda_nightly_upload_organization: my-alternative-organization