GHA: Add ppa:ubuntu-toolchain-r/test for gcc-10 #121

Job	Run time
Select platforms	3s
linux-x64-hs-nopch	0s
linux-x64-hs-zero	0s
linux-x64-hs-minimal	0s
linux-x64-hs-optimized	0s
linux-x86	0s
macos-x64	0s
windows-aarch64	0s
docs	0s
macos-aarch64	0s
linux-x64 / build	46s
windows-x64 / build (release)	6m 44s
windows-x64 / build (debug, --with-debug-level=fastdebug, -debug)	6m 40s
linux-x86	0s
macos-x64	0s
linux-x64	0s
linux-cross-compile	0s
windows-x64	1s
Remove bundle artifacts	3s
	14m 17s

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