Fix case of .tsbuildinfo in .gitignore (#32737)

The docs at https://www.typescriptlang.org/tsconfig/#tsBuildInfoFile are
inconsistent, but I'm positive now that the file name is all-lowercase.

Author: silverwind

.gitignore

@@ -28,7 +28,7 @@ _testmain.go
 *.exe
 *.test
 *.prof
-*.tsbuildInfo
+*.tsbuildinfo
 
 *coverage.out
 coverage.all