build: Tidy up scripts

[ee7]

This commit allows us to add shellcheck to CI in a later commit.

Changes:

• Double-quote variable expansions (resolves SC2086 shellcheck
  warnings).
• Use lowercase for script-scoped variables, leaving uppercase for
  environmental variables.
• Prefer "${my_variable}" to "$my_variable".
• Resolve SC2035 warning in bin/format.

shellcheck action output after this commit:

Run ludeeus/action-shellcheck@master
Files: ./.github/bin/publish-release ./.github/bin/create-artifact ./.github/bin/linux-install-build-tools ./.github/bin/build ./scripts/fetch-configlet_v3 ./bin/release ./bin/format
Excluded: ! -path *./.git/* ! -path *.go ! -path */mvnw
Options: 
Status code: 0

And before this commit:

In ./.github/bin/publish-release line 3:
VERSION=$(echo $REF | cut -d "/" -f3)
Error:                ^--^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
VERSION=$(echo "$REF" | cut -d "/" -f3)


In ./.github/bin/publish-release line 5:
gh release create $VERSION
Error:                   ^------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
gh release create "$VERSION"


In ./.github/bin/publish-release line 6:
gh release upload $VERSION $ARTIFACT_FILE
Error:                   ^------^ SC2086: Double quote to prevent globbing and word splitting.
                           ^------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
gh release upload "$VERSION" "$ARTIFACT_FILE"

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...

In ./.github/bin/create-artifact line 11:
    7z a $ARTIFACT_FILE $BINARY_NAME.exe
Error:          ^------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    7z a "$ARTIFACT_FILE" $BINARY_NAME.exe


In ./.github/bin/create-artifact line 15:
    tar -cvzf $ARTIFACT_FILE $BINARY_NAME
Error:               ^------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    tar -cvzf "$ARTIFACT_FILE" $BINARY_NAME


In ./.github/bin/create-artifact line 19:
    tar -cvzf $ARTIFACT_FILE $BINARY_NAME
Error:               ^------------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
    tar -cvzf "$ARTIFACT_FILE" $BINARY_NAME

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...

In ./bin/release line 26:
bump --v --$BUMP "$MESSAGE"
Error:            ^---^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
bump --v --"$BUMP" "$MESSAGE"

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...

In ./bin/format line 3:
nimpretty **/*.nim
Error:           ^-- SC2035: Use ./*glob* or -- *glob* so names with dashes won't become options.

For more information:
  https://www.shellcheck.net/wiki/SC2035 -- Use ./*glob* or -- *glob* so name...
Files: ./.github/bin/publish-release ./.github/bin/create-artifact ./.github/bin/linux-install-build-tools ./.github/bin/build ./scripts/fetch-configlet_v3 ./bin/release ./bin/format
Excluded: ! -path *./.git/* ! -path *.go ! -path */mvnw
Options: 
Status code: 1
Error: Process completed with exit code 1.