drivers: timer: nrf_rtc: fix TICKLESS=n processing

[pabigot]

Some kernel tests use CONFIG_TICKLESS_KERNEL=n with
CONFIG_SYS_CLOCK_TICKS_PER_SEC=1 to detect when a test runs longer
than 1 second. These tests break if a tick is announced every time a
timeout occurs. Only announce if the measured duration since the last
tick is at least the duration of a tick.

Fixes #24660

[zephyrbot]

All checks passed.

checkpatch (informational only, not a failure)

-:10: WARNING:LONG_LINE: line over 80 characters
#10: FILE: drivers/timer/nrf_rtc_timer.c:180:
+	z_clock_announce(IS_ENABLED(CONFIG_TICKLESS_KERNEL) ? dticks : (dticks > 0));

- total: 0 errors, 1 warnings, 8 lines checked

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NOTE: Ignored message types: AVOID_EXTERNS BRACES CONFIG_EXPERIMENTAL CONST_STRUCT DATE_TIME FILE_PATH_CHANGES MINMAX NETWORKING_BLOCK_COMMENT_STYLE PRINTK_WITHOUT_KERN_LEVEL SPDX_LICENSE_TAG SPLIT_STRING VOLATILE

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