tests: go fix instead of modernize

[murfffi]

also bumps testify and go patch version

[gemini-code-assist]

Code Review

This pull request updates the Go version to 1.26.2 and the testify dependency to v1.11.1. It also replaces the modernize tool with go fix in the Makefile. A critical issue was identified in the Makefile change: the go fix command does not support the -diff flag, and the current check logic is ineffective for detecting changes. It is recommended to use go fix followed by git diff --exit-code to properly verify that no migrations are pending.

[gemini-code-assist]

The go fix command does not support a -diff flag. Additionally, go fix modifies files in-place and is silent on success, so test -z will not detect changes. This check is also fragile: if go fix fails (e.g., due to the invalid flag), the error usually goes to stderr, making test -z pass incorrectly.

Note that go fix is not a direct replacement for the modernize tool. modernize checks for new language features (like any, min/max), while go fix is for legacy API migrations. If you want to verify no changes are needed, use the git diff pattern:

	go fix ./...
	git diff --exit-code