Fixed tiny spelling error in NavigationAgent2D docs #8210

Job	Run time
📊 Static checks / Code style, file formatting, and docs	46s
🍎 macOS / Editor (target=editor, tests=yes)	4m 48s
🍎 macOS / Template (target=template_release)	4m 35s
🐧 Linux / Editor w/ Mono (target=editor)	5m 8s
🐧 Linux / Editor with doubles and GCC sanitizers (target=editor, tests=yes, dev_build=yes, scu_build=yes, precision=double, use_asan=yes, use_ubsan=yes, linker=gold)	12m 48s
🐧 Linux / Editor with clang sanitizers (target=editor, tests=yes, dev_build=yes, use_asan=yes, use_ubsan=yes, use_llvm=yes, linker=lld)	7m 11s
🐧 Linux / Editor with ThreadSanitizer (target=editor, tests=yes, dev_build=yes, use_tsan=yes, use_llvm=yes, linker=lld)	7m 31s
🐧 Linux / Template w/ Mono (target=template_release)	2m 4s
🐧 Linux / Minimal template (target=template_release, everything disabled)	1m 3s
🤖 Android / Template (target=template_release)	4m 52s
🍏 iOS / Template (target=template_release)	3m 36s
🌐 Web / Template (target=template_release)	1m 16s
🏁 Windows / Editor (target=editor, tests=yes)	9m 11s
🏁 Windows / Template (target=template_release)	9m 13s
🪲 Godot CPP / Build and test Godot CPP	11m 38s
	1h 25m 40s

Provide feedback