Yes. Since 1859, the temperatures have increased, the temperature in the hottest month of the year (January) has increased, and the number of days each year with a low temperature above 21°C (70°F) has increased.
Although the temperature at Sydney during much of the year is fine for creeping bentgrass, the amount of heat stress on the grass in the summer seems to be, in an average summer of today, more than in an average summer many years ago.
First, the average annual temperatures since 1859.
Then, a look at the trend in average temperatures during the hottest month of summer -- January.
What really puts stress on creeping bentgrass is high nighttime temperatures, and this can be assessed by counting the days with a low temperature higher than 21°C. Since about 1960, the trend is to have more days with low temperatures above 21°C.
I've also made charts with the same data on Plotly. These interactive charts use the D3.js library and the values are displayed on the screen when one hovers the cursor over that point on the chart.
Sydney duration of summer heat stress -- days with low temperature above 21°C: