Closes gh-15070

Previously, a temporary .writing file could be found and an attempt made to
access its contents. If the temporary file was deleted between it being found
and its contents being read, the test would fail with a FileNotFoundException.

This commit updates the test to ignore .writing files so that it will only
examine the contents of the final file once Integration has finished
writing it an atomically moved it to its final location.

* gh-15163:
  Polish "Auto-configure Spring Session's cookie serializer"
  Auto-configure Spring Session's cookie serializer

Closes gh-15163

See gh-15163

Closes gh-15305

Closes gh-15186

Closes gh-15189

Closes gh-15188

Closes gh-15301

See gh-15271

Closes gh-15094

Closes gh-15180

Closes gh-15171

Closes gh-15293

Closes gh-15292

Closes gh-15204

Closes gh-15286

Closes gh-15227

* pr/15206:
  Polish "Perform best effort to retrieve DataSourceProxy"
  Perform best effort to retrieve DataSourceProxy