bump MSRV to 1.75 #97

Job	Run time
Build the main image for geo and proj (1.70)	4m 44s
Build the main image for geo and proj (1.75)	4m 33s
Build the main image for geo and proj (1.78)	4m 48s
Build the main image for geo and proj (1.79)	4m 38s
Build dependent images for geo and proj (geo-ci, git clone https://github.com/georust/geo && cd g...	1m 19s
Build dependent images for geo and proj (geo-ci, git clone https://github.com/georust/geo && cd g...	1m 39s
Build dependent images for geo and proj (geo-ci, git clone https://github.com/georust/geo && cd g...	1m 26s
Build dependent images for geo and proj (geo-ci, git clone https://github.com/georust/geo && cd g...	1m 38s
Build dependent images for geo and proj (proj-ci, git clone https://github.com/georust/proj && cd...	1m 38s
Build dependent images for geo and proj (proj-ci, git clone https://github.com/georust/proj && cd...	1m 37s
Build dependent images for geo and proj (proj-ci, git clone https://github.com/georust/proj && cd...	1m 25s
Build dependent images for geo and proj (proj-ci, git clone https://github.com/georust/proj && cd...	1m 39s
Build dependent images for geo and proj (proj-ci-without-system-proj, git clone https://github.co...	1s
Build dependent images for geo and proj (proj-ci-without-system-proj, git clone https://github.co...	1m 41s
Build dependent images for geo and proj (proj-ci-without-system-proj, git clone https://github.co...	1m 37s
Build dependent images for geo and proj (proj-ci-without-system-proj, git clone https://github.co...	1m 38s
	36m 1s

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