Update cheatsheets

tldr/pg_test_fsync

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+---
+syntax: markdown
+tags: [tldr, common]
+source: https://github.com/tldr-pages/tldr.git
+---
+# pg_test_fsync
+
+> Determine the fastest wal_sync_method on your system.
+> More information: <https://www.postgresql.org/docs/current/pgtestfsync.html>.
+
+- Run the default fsync benchmark (5 seconds):
+
+`pg_test_fsync`
+
+- Specify a custom test duration:
+
+`pg_test_fsync {{[-s|--secs-per-test]}} {{seconds}}`
+
+- Use a specific filename (it must be in same file system that the pg_wal directory is or will be placed in):
+
+`pg_test_fsync {{[-f|--filename]}} {{path/to/file}}`