Update security policy regarding backporting patches (#1961) #1002

Job	Run time
Linux.1: Release / steps	13m 46s
Linux.2: Debug / steps	24m 20s
Linux.4: threads=OFF / steps	12m 48s
Linux.3: static / steps	13m 58s
Linux.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal deflate / steps	4m 1s
Linux.6: custom namespace / steps	14m 2s
Linux.7: clang / steps	14m 7s
Linux.8: vfx2023 / steps	13m 28s
macOS.1: Release / steps	11m 0s
macOS.2: Debug / steps	21m 24s
macOS.3: static / steps	10m 32s
macOS.4: threads=OFF / steps	7m 59s
macOS.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal imath+deflate / steps	1m 36s
macOS.6: macos-13 / steps	21m 54s
Windows.1: Release / steps	13m 8s
Windows.2: Debug / steps	40m 42s
Windows.3: static / steps	12m 28s
Windows.4: threads=OFF / steps	13m 19s
Windows.5: pkgconfig=OFF, examples=OFF, tools=OFF, docs=OFF, internal imath+deflate / steps	1m 41s
Windows.6: vfx2022 / steps	14m 49s
	4h 41m 2s

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