workflows/cmake.yml:add tests for recent gcc versions;migrate to checkoutv3

[andy5995]

fixes #247

[andy5995]

When I added include(FindCurl) I started getting these errors:

-- Found CPPUNIT: /usr/lib/libcppunit.so  
-- ** Searching for library: FriBiDi...
-- Using FriBiDi: /usr/lib/libfribidi.so
-- Checking for one of the modules 'streflop-sse'
-- Checking for one of the modules 'streflop'
-- Search for Library STREFLOP result =  libs:  include dirs: 
-- EXTERNAL_LIBS = [/usr/lib/libcppunit.so;/usr/lib/libSDL2main.a;/usr/lib/libSDL2.so;/usr/lib/libfribidi.so;glib-2.0]
-- ***Note: The final output path for the MegaGlest engine will be [/home/andy/src/megaglest-source/mk/linux/]
-- **Found game data.
-- =====> Found Define: STREFLOP_SSE
-- =====> Found Define: HAS_GCC_BACKTRACE
-- Configuring incomplete, errors occurred!
See also "/home/andy/src/megaglest-source/mk/linux/build/CMakeFiles/CMakeOutput.log".
See also "/home/andy/src/megaglest-source/mk/linux/build/CMakeFiles/CMakeError.log".
ERROR: CMAKE failed.

When I searched the 2 log files mentioned, there were no instances of 'curl' or 'module'.

I fixed it by using the correct CASE mentioned in the FindCURL cmake docs.

Anyway, including the module didn't fix #251 unfortunately.