fix: Add flush before rewind in Tempfile tests

Add explicit f.flush call after f.write and before f.rewind in all
Tempfile tests to ensure data is flushed from user-space buffer to disk
before File.read reads the file. This prevents potential intermittent
test failures due to buffered data not being visible to subsequent reads.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: facundofarias

test/configuration_test.rb

@@ -40,6 +40,7 @@ def test_from_file_with_all_fields
 
     Tempfile.create(['config', '.json']) do |f|
       f.write(JSON.generate(config_data))
+      f.flush
       f.rewind
 
       config = Deploy::Configuration.from_file(f.path)
@@ -62,6 +63,7 @@ def test_from_file_without_websocket_hostname
 
     Tempfile.create(['config', '.json']) do |f|
       f.write(JSON.generate(config_data))
+      f.flush
       f.rewind
 
       config = Deploy::Configuration.from_file(f.path)
@@ -80,6 +82,7 @@ def test_from_file_raises_on_missing_file
   def test_from_file_raises_on_invalid_json
     Tempfile.create(['config', '.json']) do |f|
       f.write('invalid json {')
+      f.flush
       f.rewind
 
       assert_raises(JSON::ParserError) do