chore: modernize CI and update Go toolchain

- Bump Go from 1.19 to 1.26 and update all dependencies
- Rewrite CI workflow with matrix strategy (Linux, macOS, Windows)
- Update GitHub Actions to current versions (checkout@v4, setup-go@v5)
- Update CodeQL actions from v1 to v3
- Fix cross-platform bug in mock/path.go (path.Join -> filepath.Join)
- Clean up dependabot config (weekly schedule, remove stale ignore)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

vendor/github.com/kevinburke/ssh_config/CHANGELOG.md

@@ -1,7 +1,34 @@
 # Changes
 
-## Version 1.2
+## Unreleased
 
+- Implement Match support. Most of the Match spec is implemented, including
+`Match host`, `Match originalhost`, `Match user`, `Match localuser`, and `Match
+all`. `Match exec` is not yet implemented.
+
+- Add SECURITY.md
+
+- Add Dependabot configuration
+
+## Version 1.4 (released August 19, 2025)
+
+- Remove .gitattributes file (which was used to test different line endings, and
+caused issues in some build environments). Store tests/dos-lines as CRLF in git
+directly instead.
+
+## Version 1.3 (released February 20, 2025)
+
+- Add go.mod file (although this project has no dependencies).
+
+- config: add UserSettings.ConfigFinder
+
+- Various updates to CI and build environment
+
+## Version 1.2 (released March 31, 2022)
+
+- config: add DecodeBytes to directly read a byte array.
+
+- Strip trailing whitespace from Host declarations and key/value pairs.
 Previously, if a Host declaration or a value had trailing whitespace, that
 whitespace would have been included as part of the value. This led to unexpected
 consequences. For example:
@@ -17,3 +44,5 @@ unintuitive.
 
 Instead, we strip the trailing whitespace in the configuration, which leads to
 more intuitive behavior.
+
+- Add fuzz tests.