lib/storage: properly release parts inMerge lock (#3711)

if storage doesn't have enough disk space, finalDedupWatcher holds inMerge lock for all parts and never release it until storage restart

docs/CHANGELOG.md

@@ -15,6 +15,7 @@ The following tip changes can be tested by building VictoriaMetrics components f
 
 ## v1.79.x long-time support release (LTS)
 
+* BUGFIX: release `inMerge` parts lock properly at `finalDedupWatcher`. It prevented partition merges until storage restart if storage didn't have enough disk space for final deduplication and down-sampling.
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): update API version for [ec2_sd_configs](https://docs.victoriametrics.com/sd_configs.html#ec2_sd_configs) to fix [the issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3700) with missing `__meta_ec2_availability_zone_id` attribute.
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): [dockerswarm_sd_configs](https://docs.victoriametrics.com/sd_configs.html#dockerswarm_sd_configs): apply `filters` only to objects of the specified `role`. Previously filters were applied to all the objects, which could cause errors when different types of objects were used with filters that were not compatible with them. See [this issue](https://github.com/VictoriaMetrics/VictoriaMetrics/issues/3579).
 * BUGFIX: [vmagent](https://docs.victoriametrics.com/vmagent.html): suppress all the scrape errors when `-promscrape.suppressScrapeErrors` is enabled. Previously some scrape errors were logged even if `-promscrape.suppressScrapeErrors` flag was set.

lib/storage/partition.go

@@ -837,6 +837,7 @@ func (pt *partition) ForceMergeAllParts() error {
 	if newPartSize > maxOutBytes {
 		freeSpaceNeededBytes := newPartSize - maxOutBytes
 		forceMergeLogger.Warnf("cannot initiate force merge for the partition %s; additional space needed: %d bytes", pt.name, freeSpaceNeededBytes)
+		pt.releasePartsToMerge(pws)
 		return nil
 	}