UTC_OFFSET_FORMAT: use const blocks around function calls #1724

Job	Run time
Clippy	49s
Type-check benchmarks	13s
Type checking (MSRV, no_std)	3m 57s
Coverage	51s
Type checking (MSRV, std_no_offset)	5m 35s
Cross-build	31s
Documentation	15s
Type checking (MSRV, std_with_offset)	4m 27s
Formatting	19s
Type checking (stable, no_std)	55s
Test (miri)	16m 33s
Type checking (stable, std_no_offset)	2m 21s
Type checking (stable, std_with_offset)	1m 28s
Test (Ubuntu, MSRV)	3m 56s
Test (Windows, MSRV)	5m 24s
Test (MacOS, MSRV)	3m 20s
Test (Ubuntu, stable)	44s
Test (Windows, stable)	2m 57s
Test (MacOS, stable)	1m 20s
Publish docs	0s
	55m 55s

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