testing/fast_float: build tests with check only

testing/fast_float/APKBUILD

@@ -15,7 +15,7 @@ build() {
 	cmake -B builddir -G Ninja \
 		-DCMAKE_INSTALL_PREFIX=/usr \
 		-DCMAKE_BUILD_TYPE=Release \
-		-DFASTFLOAT_TEST=ON \
+		-DFASTFLOAT_TEST="$(want_check && echo ON || echo OFF)" \
 		-DSYSTEM_DOCTEST=ON
 	cmake --build builddir
 }