bigquery: civil.DateTime and civil.Time fail to insert

**Client**

BigQuery

**Environment**

distroless docker on GKE

**Go Environment**

$ go version go1.22.4 darwin/arm64
$ ❯ go env
GO111MODULE=''
GOARCH='arm64'
GOBIN=''
GOCACHE='/Users/lgr/Library/Caches/go-build'
GOENV='/Users/lgr/Library/Application Support/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFLAGS=''
GOHOSTARCH='arm64'
GOHOSTOS='darwin'
GOINSECURE=''
GOMODCACHE='/Users/lgr/workspace/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='darwin'
GOPATH='/Users/lgr/workspace/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go/'
GOSUMDB='sum.golang.org'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/darwin_arm64'
GOVCS=''
GOVERSION='go1.22.4'
GCCGO='gccgo'
AR='ar'
CC='clang'
CXX='clang++'
CGO_ENABLED='1'
GOMOD='/Users/lgr/workspace/go/xxxx'
GOWORK=''
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
PKG_CONFIG='pkg-config'
GOGCCFLAGS='-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -ffile-prefix-map=/var/folders/ry/1805fhs14_n982jppzrh0v0h0000gn/T/go-build1957741136=/tmp/go-build -gno-record-gcc-switches -fno-common'

**Code**

```go
import (
"strings"
"testing"

"cloud.google.com/go/bigquery"
"cloud.google.com/go/civil"
)

func TestCivilDateTimeString(t *testing.T) {

dt1, _ := civil.ParseDateTime("2006-01-02T15:04:05.99999")
dt2, _ := civil.ParseDateTime("2006-01-02T15:04:05.999999")
dt3, _ := civil.ParseDateTime("2006-01-02T15:04:05.9999999")
tests := []struct {
d civil.DateTime
}{
{dt1},
{dt2},
{dt3},
}

for _, tt := range tests {
formatted := bigquery.CivilDateTimeString(tt.d)
i := strings.LastIndex(formatted, ".")
microSecondLength := len(formatted[i+1:])

t.Logf("Raw: %v\tFormatted: %s \tMicroSecondLength: %d", tt.d, formatted, microSecondLength)
if microSecondLength > 6 {
t.Errorf("Microsecond length is %d, expected <= 6", microSecondLength)
}
}
}
```

**Expected behavior**

A `civil.DateTime` or `civil.Time` formatted with the functions `bigquery.CivilDateTimeString` or `bigquery.CivilTimeString` should be insertable into bigquery with the `DATETIME` and `TIME` datatypes.

**Actual behavior**

If the Nanoseconds of a `civil.Time` are rounded up (like `dt3` above) bigquery does not accept the value and reponds with an error like this:
```
row insertions failed (insertion of row [insertID: "EzTAFi6QkJAggrZdB0rKdv18oxQ"; insertIndex: 927] failed with error: {Location: "timestamp"; Message: "Invalid datetime string \"2024-07-02 05:12:21.1000000\""; Reason: "invalid"}
```

The reason seems to be that the string format accepted by `DATETIME` and `TIME` expects a maximum of 6 fractional digits cd. [Data type docs](https://cloud.google.com/bigquery/docs/reference/standard-sql/data-types#datetime_type)

However, `bigquery.CivilTimeString` can produce more fractional digits, as can be seen in the test above.

**Context**

For me the error occured while using the `Uploader` and saving structs that use `civil.DateTime` as timestamp. I tracked the error down to the `bigquery.CivilTimeString` function.