UTC_OFFSET_FORMAT: use const blocks around function calls #1719

Job	Run time
Clippy	1m 32s
Coverage	1m 8s
Type checking (MSRV, no_std)	2m 9s
Type-check benchmarks	33s
Type checking (MSRV, std_no_offset)	2m 10s
Cross-build	1m 14s
Documentation	21s
Type checking (MSRV, std_with_offset)	2m 9s
Type checking (stable, no_std)	1m 17s
Formatting	12s
Type checking (stable, std_no_offset)	2m 8s
Test (miri)	2m 9s
Test (Ubuntu, MSRV)	2m 12s
Type checking (stable, std_with_offset)	1m 32s
Test (Windows, MSRV)	2m 0s
Test (MacOS, MSRV)	2m 10s
Test (Ubuntu, stable)	1m 4s
Test (Windows, stable)	1m 59s
Test (MacOS, stable)	52s
Publish docs	1s
	28m 52s

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