Eliminate macOS sprintf warning

AppleClang 14.0.0.14000029 warns about a potential security problem
while invoking the sprintf C function:

    internal/ceres/fixed_array_test.cc:469:3: warning: 'sprintf' is deprecated: This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead. [-Wdeprecated-declarations]
      sprintf(buf.data(), "foo");  // NOLINT(runtime/printf)
      ^
    /Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/usr/include/stdio.h:188:1: note: 'sprintf' has been explicitly marked deprecated here
    __deprecated_msg("This function is provided for compatibility reasons only.  Due to security concerns inherent in the design of sprintf(3), it is highly recommended that you use snprintf(3) instead.")
    ^
    /Applications/Xcode_14.2.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX13.1.sdk/usr/include/sys/cdefs.h:215:48: note: expanded from macro '__deprecated_msg'
            #define __deprecated_msg(_msg) __attribute__((__deprecated__(_msg)))

Replace sprintf by snprintf to avoid this deprecation warning.

Change-Id: I6870c0bd4e390388d1d7bcec082cee272b234eba
diff --git a/internal/ceres/fixed_array_test.cc b/internal/ceres/fixed_array_test.cc
index d6c5605..66b3fbf 100644
--- a/internal/ceres/fixed_array_test.cc
+++ b/internal/ceres/fixed_array_test.cc
@@ -466,7 +466,7 @@
 //     will always overflow destination buffer [-Werror]
 TEST(FixedArrayTest, AvoidParanoidDiagnostics) {
   ceres::internal::FixedArray<char, 32> buf(32);
-  sprintf(buf.data(), "foo");  // NOLINT(runtime/printf)
+  snprintf(buf.data(), 32, "foo");
 }
 
 TEST(FixedArrayTest, TooBigInlinedSpace) {