chore: do not use sentinel errors when unneeded

- main reason being it's a burden to always define sentinel errors at global scope, wrap them with `%w` instead of using a string directly
- only use sentinel errors when it has to be checked using `errors.Is`
- replace all usage of these sentinel errors in `fmt.Errorf` with direct strings that were in the sentinel error
- exclude the sentinel error definition requirement from .golangci.yml
- update unit tests to use ContainersError instead of ErrorIs so it stays as a "not a change detector test" without requiring a sentinel error

internal/healthcheck/client.go

@@ -2,15 +2,12 @@ package healthcheck
 
 import (
 	"context"
-	"errors"
 	"fmt"
 	"io"
 	"net/http"
 	"time"
 )
 
-var ErrHTTPStatusNotOK = errors.New("HTTP response status is not OK")
-
 type Client struct {
 	httpClient *http.Client
 }
@@ -41,6 +38,6 @@ func (c *Client) Check(ctx context.Context, url string) error {
 	if err != nil {
 		return err
 	}
-	return fmt.Errorf("%w: %d %s: %s", ErrHTTPStatusNotOK,
+	return fmt.Errorf("HTTP response status is not OK: %d %s: %s",
 		response.StatusCode, response.Status, string(b))
 }