Enable more golang-ci linters

[timvaillancourt]

Description

This PR enables a number of linters in the golang-ci Actions job:

• contextcheck - check the function whether use a non-inherited context
• durationcheck - check for two durations multiplied together
• errname - Checks that sentinel errors are prefixed with the Err and error types are suffixed with the Error
• execinquery - execinquery is a linter about query string checker in Query function which reads your Go src files and warning it finds
• gofmt - Gofmt checks whether code was gofmt-ed. By default this tool runs with -s option to check for code simplification
• ifshort - Checks that your code uses short syntax for if-statements whenever possible
• misspell - Finds commonly misspelled English words in comments
• nilerr - Finds the code that returns nil even if it checks that the error is not nil
• nolintlint - Reports ill-formed or insufficient nolint directives
• nosprintfhostport - Checks for misuse of Sprintf to construct a host with port in a URL
• prealloc - Finds slice declarations that could potentially be pre-allocated
• unconvert - Remove unnecessary type conversions
• wastedassign - wastedassign finds wasted assignment statements
• whitespace - Tool for detection of leading and trailing whitespace

This PR also contains fixes for linter warnings this introduced, mostly for ifshort, unconvert and wastedassign

In case this PR introduced Go code changes:

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors.

[RainbowDashy]

I wonder why these lines are not spotted by nilerr.

if err := this.finalCleanup(); err != nil {
	return nil
}

https://github.com/timvaillancourt/gh-ost/blob/baa85a5fe14fd20dc3cc7cf03f880f3800365acb/go/logic/migrator.go#L443-L445