fix(acceptance): use a more standard git commit time format

i think this might be an issue with the sha256 of the tile
I would think it would also change the source_revision but maybe not

internal/acceptance/workflows/scenario/step_funcs_tile_source_code.go

@@ -131,8 +131,8 @@ func copyTileDirectory(dir, tileDirectory string) (string, error) {
 	if err := executeAndWrapError(testTileDir, env, "git", "add", "."); err != nil {
 		return "", fmt.Errorf("tile path is not a repository: adding initial files failed: %w", err)
 	}
-	env = updateEnvVar(env, "GIT_AUTHOR_DATE", "1112937193 -0700")
-	env = updateEnvVar(env, "GIT_COMMITTER_DATE", "1112937193 -0700")
+	env = updateEnvVar(env, "GIT_AUTHOR_DATE", "Thu, 07 Apr 2005 22:13:13")
+	env = updateEnvVar(env, "GIT_COMMITTER_DATE", "Thu, 07 Apr 2005 22:13:13")
 	if err := executeAndWrapError(testTileDir, env, "git", "commit", "-m", "initial commit"); err != nil {
 		return "", fmt.Errorf("tile path is not a repository: adding initial files failed: %w", err)
 	}